Laser irradiation apparatus, laser irradiation method, and method for manufacturing a semiconductor device

ABSTRACT

YAG laser can simultaneously emit a plurality of laser beams having different wavelengths from each other. By simultaneously irradiating the laser beams having different wavelengths from each other to a same region of a non-single crystal semiconductor film, an interference influence is suppressed to obtain a more uniform laser beam. For example, by simultaneously generating second and third harmonics of YAG laser to irradiate the same region through suitable optical system, a laser beam having higher uniformity and having an energy in which interference is highly suppressed is obtained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus for manufacturing asemiconductor device having a circuit structured with a thin filmtransistor. For example, the invention relates to an apparatus formanufacturing an electro-optical device, typically a liquid crystaldisplay device, and the structure of electric equipment mounted withsuch an electro-optical device as a component. Note that throughout thisspecification, the semiconductor device indicates general devices thatmay function by use of semiconductor characteristics, and that the aboveelectro-optical device and electric equipment are categorized as thesemiconductor device.

[0003] 2. Description of the Related Art

[0004] In recent years, the technique of crystallizing and improving thecrystallinity of an amorphous semiconductor film or a crystallinesemiconductor film (a semiconductor film having a crystallinity which ispolycrystalline or microcrystalline, but is not a single crystal), inother words, a non-single crystal semiconductor film, formed on aninsulating substrate such as a glass substrate by laser annealing, hasbeen widely researched. Silicon film is often used as the abovesemiconductor film.

[0005] Comparing a glass substrate with a quartz substrate, which isoften used conventionally, the glass substrate has advantages oflow-cost and great workability, and can be easily formed into a largesurface area substrate. This is why the above research is performed.Also, the reason for preferably using a laser for crystallizationresides in that the melting point of a glass substrate is low. The laseris capable of imparting high energy only to the non-single crystallinefilm without causing much change in the temperature of the substrate.

[0006] The crystalline silicon film is formed from many crystal grains.Therefore, it is called a polycrystalline silicon film or apolycrystalline semiconductor film. A crystalline silicon film formed bylaser annealing has high mobility. Accordingly, it is actively used in,for example, monolithic type liquid crystal electro-optical deviceswhere thin film transistors (TFTs) are formed using this crystallinesilicon film and used as TFTs for driving pixels and driving circuitsformed on one glass substrate.

[0007] Furthermore, a method of performing laser annealing is one inwhich a laser beam emitted from a pulse oscillation type excimer laser,which is large in output, is processed by an optical system so that thelaser beam thereof becomes a linear shape that is 10 cm long or greateror a square spot that is several cm square at an irradiated surface tothereby scan the laser beam (or relatively move the irradiation positionof the laser beam to the irradiated surface). Because this method ishigh in productivity and industrially excellent, it is being preferablyemployed. A laser beam that has been linearized into a laser beam thatis 10 cm long or greater at the irradiated surface is referred as alinear laser beam throughout the present specification.

[0008] Different from when using a spot shape (square) laser beam whichrequires a front, back, left, and right scan, when using the linearlaser beam, in particular, the entire irradiated surface can beirradiated by the laser beam which requires only scanning at a rightangle direction to the linear direction of the linear laser beam,resulting in the attainment of a high productivity. To scan in adirection at a right angle to the linear direction is the most effectivescanning direction. Because a high productivity can be obtained, usingthe laser beam that is emitted from the pulse oscillation type excimerlaser and processing it into a linear laser beam by an appropriateoptical system for laser annealing at present is becoming a mainstream.

[0009] Shown in FIGS. 1A and 1B is an example of the structure of anoptical system for linearizing the sectional shape of a laser beam onthe irradiated surface. This structure is a very general one and allaforementioned optical systems conform to the structure of the opticalsystem shown in FIGS. 1A to 1B. This structure of the optical system notonly transforms the sectional shape of the laser beam into a linearshape, but also homogenizes the energy of the laser beam in theirradiated surface at the same time. Generally, an optical system thathomogenizes the energy of a beam is referred to as a beam homogenizer.

[0010] If the excimer laser, which is ultraviolet light, is used as thelight source, then the core of the above-mentioned optical system may bemade of, for example, entirely quartz. The reason for using quartzresides in that a high transmittance can be obtained. Further, it isappropriate to use a coating in which a 99% or more transmittance can beobtained with respect to a wavelength of the excimer laser that is used.

[0011] The side view of FIG. 1A will be explained first. Laser beamemitted from a laser oscillator 101 is split at a right angle directionto the advancing direction of the laser beam by cylindrical lens arrays102 a and 102 b. The right angle direction is referred to as alongitudinal direction throughout the present specification. When amirror is placed along the optical system, the laser beams in thelongitudinal direction will curve in the direction of light curved bythe mirror. These laser beams in this structure are split into 4 beams.The split laser beams are then converged into 1 beam by a cylindricallens 104. Then, the converged laser beam are split again and reflectedat a mirror 107. Thereafter, the split laser beams are again convergedinto 1 beam at an irradiated surface 109 by a doublet cylindrical lens108. A doublet cylindrical lens is a lens that is constructed of 2pieces of cylindrical lenses. Thus, the energy in the width direction ofthe linear laser beam is homogenized and the length of the widthdirection of the linear laser beam is also determined.

[0012] The top view of FIG. 1B will be explained next. Laser beamemitted from the laser oscillator 101 is split at a right angledirection to the advancing direction of the laser beam and at a rightangle direction to the longitudinal direction by a cylindrical lensarray 103. The right angle direction is called a vertical directionthroughout the present specification. When a mirror is placed along theoptical system, the laser beams in the vertical direction will curve inthe direction of light curved by the mirror. The laser beams in thisstructure is split into 7 beams. Thereafter, the split laser beams areconverged into 1 beam at the irradiated surface 109 by the cylindricallens 104. Thus, homogenization of the energy in the longitudinaldirection of the linear laser beam is made and the length of thelongitudinal direction is also determined.

[0013] The above lenses in the optical system are made of syntheticquartz for correspondence to excimer laser. Furthermore, coating isimplemented on the surfaces of the lenses so that the excimer laser willbe well transmitted. Therefore, the transmittance of excimer laserthrough one lens is 99% or more.

[0014] By irradiating the linear laser beam linearized by the abovestructure of the optical system in an overlapping manner with a gradualshift in the width direction thereof, laser annealing is implemented tothe entire surface of a non-single crystal silicon film to therebycrystallize the non-single crystal silicon film and thus itscrystallinity can be enhanced.

[0015] A typical method of manufacturing a semiconductor film that is tobecome the object to be irradiated is shown next.

[0016] First, a 5 inch square Corning 1737 substrate having a thicknessof 0.7 mm is prepared as the substrate. Then a 200 nm-thick SiO₂ film(silicon oxide film) is formed on the substrate and a 50 nm-thickamorphous silicon film (hereinafter denoted by “a-Si film”) is formed onthe surface of the SiO₂ film. Both films are formed by employing theplasma CVD apparatus.

[0017] The substrate is exposed under an atmosphere containing nitrogengas at a temperature of 500° C. for 1 hour to thereby reduce thehydrogen concentration in the film. Accordingly, the laser resistance inthe film is remarkably improved.

[0018] The XeCl excimer laser L3308 (wavelength: 308 nm, pulse width: 30ns) manufactured by Lambda Co. is used as the laser apparatus. Thislaser apparatus generates a pulse oscillation laser and has the abilityto output an energy of 500 mJ/pulse. The size of the laser beam at theexit of the laser beam is 10×30 mm (both half-width). Throughout thepresent specification, the exit of the laser beam is defined as theperpendicular plane in the advancing direction of the laser beamimmediately after the laser beam is emitted from the laser irradiationapparatus.

[0019] The shape of the laser beam generated by the excimer laser isgenerally rectangular and is expressed by an aspect ratio which fallsunder the range of the order of 2 to 5. The intensity of the laser beamgrows stronger towards the center of the beam and indicates the Gaussiandistribution. The size of the laser beam processed by the optical systemhaving the structure shown in FIG. 1 is transformed into a 125 mm×0.4 mmlinear laser beam having a uniform energy distribution.

[0020] Based upon an experiment conducted by the present inventor, whenirradiating a laser to the above-mentioned semiconductor film, the mostsuitable overlapping pitch is approximately ,{fraction (1/10)} of thewidth (half-width) of the linear laser beam. The uniformity of thecrystallinity in the film is thus improved. In the above example, thehalf-width of the linear laser beam was 0.4 mm, and therefore the pulsefrequency of the excimer laser was set to 30 hertz and the scanningspeed was set to 1.0 mm/s to thereby irradiate the laser beam. At thispoint, the energy density in the irradiated surface of the laser beamwas set to 420 mJ/cm². The method described so far is a very generalmethod employed for crystallizing a semiconductor film by using a linearlaser beam.

[0021] When an extremely attentive observation is made to a silicon filmthat has been laser annealed by using the above-mentioned linear laserbeam, very faint interference patterns were seen in the film. The causeof the interference patterns seen in the film resides in that the laserbeam is split and assembled in 1 region, and therefore the split lightbrings about interference with each other. However, because the coherentlength of the excimer laser is about several microns to several tenthsof microns, a strong interference will not occur. As a result, theinfluence imparted by the above-mentioned interference to asemiconductor device is extremely small.

[0022] The excimer laser is large in output and capable of oscillatingpulses repetitively at a high frequency (approximately 300 hertz underthe present situation), and hence is often used in performingcrystallization of a semiconductor film. In recent years, advances havebeen made in manufacturing,low temperature poly-silicon TFTs used inliquid crystal displays. Accordingly, the excimer laser is employed inthe crystallization process of semiconductor films.

[0023] Further, the largest output of an YAG laser is remarkablyimproved. Because the YAG laser is a solid state laser, it is easier tohandle and maintain compared with the excimer laser which is a gaslaser. Therefore, in the crystallization process of a semiconductorfilm, if the YAG laser is substituted for the excimer laser, anastounding improvement in cost performance can be expected. On the basisof the background such as the above, the present applicant is makingan-examination in the possibility of using the YAG laser in thecrystallization process of a semiconductor film.

[0024] It is known that the YAG laser outputs a laser beam having awavelength of 1065 nm as the fundamental wave. The absorptioncoefficient of this laser beam with respect to silicon films isextremely low, and therefore the laser beam as it is cannot be used inthe crystallization process of the a-Si film, which is one of thesilicon films. However, the laser beam, i.e., the fundamental wave, canbe modulated into having a shorter wavelength by using a non-linearoptical crystal. Due to the modulated wavelengths, the laser beam isnamed a second harmonic (wavelength 533 nm), a third harmonic(wavelength 355 nm), a fourth harmonic (wavelength 266 nm), and a fifthharmonic (wavelength 213 nm).

[0025] Since the wavelength of the second harmonic is 533 nm, it hassufficient absorption to an a-Si film that is about 50 nm thick, andhence can be used in crystallizing the a-Si film. In addition, the thirdharmonic, the fourth harmonic, and the fifth harmonic also have a highabsorption to the above-mentioned a-Si film, and therefore similarcrystallization can be performed.

[0026] The largest output of the second harmonic from the currentgeneral-purpose YAG laser is about 1500 mJ/pulse. Further, the largestoutput of the third harmonic thereof is about 750 mJ/pulse and thelargest output of the fourth harmonic thereof is about 200 mJ/pulse. Thelargest output of the fifth harmonic is further lower than theaforementioned largest outputs, and thus if the fifth harmonic is usedin crystallizing the a-Si film, mass production will become extremelyworse. Taking into consideration both the output of the laser beam andits absorption to the a-Si film, at the present level, it is best to usethe second harmonic and the third harmonic.

[0027] In the case of using the YAG laser to crystallize thesemiconductor film, nonetheless, the shape of the laser beam at theirradiated surface is preferably linear for mass production.Hereinbelow, an examination is made on the possibility of applying theabove-mentioned optical system to the YAG laser without anymodifications made thereto.

[0028] First, the difference between the beam shape of the YAG laser andthe beam shape of the excimer laser will be described. The shape of thelaser beam emitted from the excimer laser is generally rectangular,whereas the shape of the laser beam emitted from the YAG laser is bothcircular and rectangular. To process a rectangular laser beam into alinear laser beam is comparatively easy since transformation is madefrom a rectangular shape to a rectangular shape. However, to transform acircular beam into a rectangular linear laser beam is comparativelydifficult. Therefore, judging from the shape of the beam only, it isbetter to use the rectangular beam emitted from the YAG laser than touse the circular beam emitted therefrom.

[0029] Hereinafter, a description will be made on the uniformity ofenergy between the beam of the YAG laser which emits the rectangularbeam and the beam of the YAG laser which emits the circular beam, and anexamination is conducted to discern which one of the YAG lasers issuitable as a substitute for the excimer laser.

[0030] The type of YAG laser which has a beam shape that is circularirradiates a strong light (flash lamp and laser diode, hereinafterdenoted by LD) for exciting a cylindrical crystal rod, thereby obtaininglaser oscillation. On the other hand, the type of YAG laser which has abeam shape that is rectangular irradiates a strong light to aparallelepiped crystal rod that structures a system called a zigzagslub, thereby obtaining laser oscillation.

[0031] Comparing the energy uniformity of the beam oscillated from theYAG laser which has a beam shape that is circular with that of theexcimer laser, the energy uniformity of the former is in general notgood. This non-uniformity of energy originates from a temperaturedistribution of the above-mentioned cylindrical crystal rod which occursfrom the application of a strong light. As can be readily surmised fromthe shape of the aforementioned cylindrical crystal rode, thetemperature of the temperature distribution thereof becomes lowertowards the exterior of the cylinder. Thus, a function similar to thatof a lens is added to the aforementioned cylindrical crystal rod,thereby worsening the energy uniformity of the beam. This phenomenon isgenerally called the thermal lens effect.

[0032] A system conceived for the purpose of restraining the abovethermal lens effect is a zigzag slub system of the YAG laser. Thestructure of the zigzag slub system of the YAG laser will be brieflyexplained with reference to FIG. 2 in the following.

[0033] The rod system YAG laser obtains laser oscillation by excitationof the cylindrical crystal called a crystal rod. However, in the case ofthe zigzag slub system YAG laser, the shape of the crystal rod isparallelepiped. A parallelepiped crystal 202 is irradiated by excitationlamps 203 a and 203 b, for example, an LD and a flash lamp, to therebyobtain laser oscillation. Electric power is supplied to the excitationlamps 203 a and 203 b from a power source 208. Furthermore, theparallelepiped crystal 202 is cooled by a cooler 207.

[0034] Arranging resonant mirrors 201 and 204 diagonally to theparallelepiped crystal 202 is a characteristic of the zigzag slubsystem. The resonant mirrors 201 and 204 are arranged parallelly in astate facing each other and sandwiching the parallelepiped crystal 202.Each of the surfaces of the parallelepiped crystal 202 and the resonantmirrors have no parallel positional relationship. By appropriatelyadjusting the positional relationship, light reflected from the resonantmirrors will advance in a zigzag way within the parallelepiped crystal.When laser is oscillated at this point in this state, a large amount oflight will exit from a side surface of the parallelepiped crystalresulting in a large lost of energy, and thus becoming unusable. Inorder to prevent this drawback, reflector mirrors 205 and 206 arearranged at the side surfaces of the parallelepiped crystal to therebyprevent light escaping from the parallelepiped crystal 202. Gold-platedmirrors, for example, may be used as the reflector mirrors 205 and 206.

[0035] By adopting the above structure, the laser beam not only passesthrough the interior portion of the parallelepiped crystal rod, but alsopasses through the exterior portion thereof. Thus, influence to thebiased laser beam of the temperature distribution of the crystal is lessthan the case of using the cylindrical crystal rod. Consequently,influence from the thermal lens effect becomes lesser thereby enhancingthe uniformity of the beam.

[0036] Thus, it can be determined from the above examination that thezigzag system YAG laser is suitable as a substitute for the excimerlaser than the type of YAG laser which employs the cylindrical crystalrod because the shape of the laser beam emitted from the zigzag systemYAG laser is similar to that of the excimer laser and the uniformity ofthe beam thereof is higher.

[0037] Next, consideration is made in regards to a difference in thecoherent length of the YAG laser and the excimer laser. As stated above,the coherent length of the excimer laser is about several microns toseveral tenths of microns, and therefore the occurrence of lightinterference when the laser beam passes through the aforementionedoptical system, which splits and then converges the laser beam into 1beam again, is thus very weak. On the other hand, the coherent length ofthe YAG laser is quite long, about 1 cm or more. Hence, the influencesof the interference due to this long coherent length of the YAG lasercannot be ignored.

[0038] If the laser beam emitted from the YAG laser is passed throughthe optical system shown in FIG. 1 to be processed into a linear laserbeam, then a linear laser beam 300 having an energy distribution withrepetitive strong and weak regions in a lattice pattern as shown in FIG.3A is formed.

[0039] The lattice pattern energy distribution is caused by the lightinterference. In FIG. 3A, darker lines 301 denotes regions where theenergy is comparatively high and blank lines 302 between the darkerlines 301 denotes regions where the energy is comparatively low.

[0040] Using the linear laser beam 300, which has a lattice patternenergy distribution, to crystallize the a-Si film will nonetheless causenon-uniform crystallization in the surface of the a-Si film. Shown inFIG. 3B is the appearance of a front surface of a silicon film 303crystallized by the linear laser beam. As described in the above, thelinear laser beam is irradiated on the a-Si film in the width directionof the linear laser beam and overlaps each other in a manner that isabout {fraction (1/10)} of the length of the width of the laser beam.Therefore, the stripes parallel to the linear direction of the linearlaser beam eliminate each other out, becoming inconspicuous. However,lines 304 and 305 that are parallel to the width direction of the laserbeam strongly remain. In FIG. 3B, darker lines 304 denotes regions wherethe energy is comparatively high and blank lines 305 between the darkerlines 304 denotes regions where the energy is comparatively low.

SUMMARY OF THE INVENTION

[0041] The present invention has been made in view of the above, andtherefore has an object thereof to select an appropriate YAG laser as asubstitute for an excimer laser used for the crystallization of asemiconductor film, and to resolve the aforementioned problem of aninterference pattern, thereby providing a laser irradiation apparatusfor attaining a polycrystalline silicon film having very little stripepatterns.

[0042] The inventors of the present invention have selected a zigzagslub system YAG laser, which has a rectangular beam shape, as theappropriate YAG laser for employment in the crystallization of asemiconductor film. In the present invention, it is important that theshape of the beam is rectangular, and there is no particular problem inusing a YAG laser of a different system. However, the present inventorconsiders the zigzag slub system as the most suitable system among thecurrent systems of the YAG laser at present. Further, the laserirradiation apparatus disclosed in the present specification is notparticularly limited to one that emits a rectangular laser beam, but alaser irradiation apparatus that emits a circular laser beam may also beused.

[0043] As a problem that occurs when the YAG laser is used incrystallizing the semiconductor film is that interference, as mentionedin the above paragraph, is liable to occur in the YAG laser comparedwith the excimer laser.

[0044] The present invention will provide a technique to suppress aninfluence of the interference pattern. As mentioned before, theoscillation wavelength of the YAG laser includes a fundamental wave(1.06 um), a second harmonic (0.53 um), a third harmonic (0.35 um), afourth harmonic, a fifth harmonic, and so forth.

[0045] Shown in FIG. 4A is a schematic view of a simplified beamhomogenizer having the second harmonic of the YAG laser as a lightsource. A fundamental wave emitted from a light source 401 is convertedinto the second harmonic by a non-linear optical element 402. Becausecomponents of the fundamental wave still remain in the laser beamconverted into the second harmonic, at a beam splitter 403, only thefundamental wave is transmitted and the second harmonic is reflected.Next, the light path of the second harmonic is bend 90 degrees by amirror 404, and then split into 2 beams by a cylindrical lens array 405.Thereafter, the split beams are converged into 1 beam at an irradiatedsurface 407 by a cylindrical lens 406. At the irradiated surface 407 atthis point, lights having equivalent wavelengths advance in oppositedirections to each other, thereby interfering with each other. Thepattern of interference that has developed in the irradiated surface 407is shown in FIG. 4B. The pattern of interference illustrated in FIG. 4Bis one in which plural patterns of wave shapes that change with time areoverlapped. Throughout the present specification, a plural number ofpatterns of interference are shown, but all will be shown in the samemethod as that of FIG. 4B.

[0046] A stationary wave is formed when lights of equivalent wavelengthsadvance in opposite direction from each other. However, in a portionwhere energy is weak, the energy thereof becomes extremely weak. Thus,when a region having an immense energy difference is formed, a massivedecline in the uniformity of crystallization by using laser is thereforeunavoidable.

[0047] Accordingly, by utilizing the characteristic of the YAG lasercapable of simultaneously emitting plural kinds of wavelengths of light,the present inventor designed a method of making the interferencepattern inconspicuous by compositing YAG lasers of differentwavelengths.

[0048] An example of a system that is capable of making the interferencepattern inconspicuous is shown in FIG. 5A. Light (fundamental wave)oscillated from a resonator 501 of the YAG laser is converted into thesecond and third harmonic, besides being converted to the fundamentalwave, via a non-linear crystal 502 for converting wavelengths. Thefundamental wave is split by a beam splitter 503 which is provided withfunctions to satisfactorily penetrate the wavelength region of thefundamental wave, and to satisfactorily reflect the other wavelengths.Lights having the second and third harmonic reflected from the beamsplitter 503 intermingled can thus be formed. Then at a beam splitter504, only the second harmonic is reflected while the third harmonic istransmitted. Finally, the advancing direction of the third harmonic isalternated by a reflector mirror 505 so that the advancing directionthereof is the same as the advancing direction of the second harmonic.

[0049] Thus, a YAG laser capable of simultaneously emitting 3 types oflights, that is, the fundamental wave, the second harmonic, and thethird harmonic, can be made through the above structure. Not much of thefundamental wave is absorbed by the silicon film, and hence is not usedin the crystallization of the silicon film. The second and thirdharmonic are used in the crystallization thereof.

[0050] Shown in FIG. 34 is a wavelength dependence of a ratio of theabsorption of light to a 55 nm-thick a-Si film formed on a glasssubstrate. As can be known from the graph, when light having awavelength of 600 nm or less is used, there is a 10 percent or moreabsorption to the silicon film. Therefore, when the present invention isapplied to a 55 nm-thick a-Si film, light having a wavelength of 600 nmor less is used.

[0051] The second harmonic is split into 2 beams by a cylindrical lensarray 506. On the other hand, the third harmonic is split into 2 beamsby a cylindrical lens array 507. The cylindrical lens arrays 506 and 507are set at positions with equivalent focal lengths. Finally, acylindrical lens 508 is arranged and the laser beam which has been splitinto 4 beams are composited to 1 region by the cylindrical lens 508.

[0052] The second harmonic and the third harmonic enter the cylindricallens 508. Therefore, though there is a few percentage of difference inthe focal length to the second harmonic and the third harmonic with eachother, there is no influence to the present experiment. Quartz, whichhas a high transmissivity to both the second harmonic and the thirdharmonic, is used as the material of the lenses. Interference occurs inan irradiated surface 509 due to the fact that the second harmonic andthe third harmonic advance in opposite directions from each other. Asimulation result of the pattern of interference formed in theirradiated surface 509 is shown in FIG. 5B. It is apparent from thegraph of FIG. 5B that nodes caused by the interference have disappeared.

[0053]FIG. 6 is a view illustrating the state of an interference thathas occurred when the second harmonic and the third harmonic havingequivalent swinging widths with each other are made to advance inopposite directions from each other at equivalent speeds. In FIG. 6, thelongitudinal axis denotes the intensity of light and the lateral axisdenotes a position. As can be understood from FIG. 6, it is apparentthat the energy distribution of light is more balanced in this case thanin the case of using only the second harmonic.

[0054] An output of the second harmonic emitted from the YAG laserhaving the structure of FIG. 5 is about twice the size of an output ofthe third harmonic. Therefore, in order to synthesize the secondharmonic and the third harmonic emitted from the YAG laser having thestructure of FIG. 5 to thereby make the interference patternsinconspicuous, it is necessary to consider synthesizing a secondharmonic that has a swinging width of {square root}{square root over ()}2 and a third harmonic that has a swinging width of 1. The simulationresult thereof is shown in FIG. 7. Making the swinging width of thesecond harmonic of FIG. 6 to {square root}{square root over ( )}2 timesis the result of FIG. 7. Similar to the result of FIG. 6, the energydistribution of light is also satisfactorily balanced in FIG. 7.

[0055] Thus, from the above results, it can be surmised that thecontrast of a strong and weak pattern of the energy caused by theinterference can be easily suppressed by synthesizing lights havingdifferent wavelengths from each other. Actually, similar results can beexpected from synthesizing the second harmonic and the fourth harmonicand synthesizing the third harmonic and the fourth harmonic. An exampleof synthesizing the second harmonic and the fourth harmonic is shown inFIG. 8, and an example of synthesizing the third harmonic and the fourthharmonic is shown in FIG. 9. It is apparent that the energy is madeuniform in both examples. Energy uniformity can also be achieved even if3 types or more different wavelengths of laser beams are mixed together.In other words, by irradiating each of the laser beams having differentwavelengths from each other to the same region and at the same time,uniformity of the laser beam in the same region can be improved.

[0056] The above-mentioned method of making the interference patterninconspicuous by synthesizing laser beams of different wavelengths isapplied to the optical system for forming linear laser beams that isillustrated in FIG. 1. The interference pattern is made inconspicuous bymaking laser beams of different wavelengths advance in oppositedirections from each other at equivalent speeds. For example, the effectof making the interference pattern inconspicuous can be obtained in anoptical system for forming linear laser beams illustrated in FIG. 10.The optical system shown in FIG. 10 is a beam homogenizer, similar tothe optical system shown in FIG. 1. The basic perspective ofconstructing the lenses in both optical systems is the same.

[0057] The role of the optical system structured as shown in FIG. 10will be explained. The aforementioned YAG laser is used as a laseroscillator. The YAG laser oscillates the second harmonic and the thirdharmonic in addition to the fundamental wave. The fundamental waveoutputted from a laser resonator 1001 is converted into the secondharmonic and the third harmonic by a non-linear optical element 1002.Components of the fundamental wave remain in the second harmonic and thethird harmonic. Next, the fundamental wave is separated by a beamsplitter 1003 while the second harmonic and the third harmonic areintroduced to a beam splitter 1004. The second harmonic and the thirdharmonic are further separated into a second harmonic and a thirdharmonic by the beam splitter 1004.

[0058] Penetrating the beam splitter 1004, the advancing direction ofthe third harmonic is bent by reflector mirrors 1005 and 1006. As aresult, the second harmonic and the third harmonic exit at obliqueopposite angle positions in the form of being parallel with each other.

[0059] The second harmonic is first split into 2 beams in the verticaldirection by a cylindrical lens array 10071, and then split into 2 beamsin the horizontal direction by a cylindrical lens array 10081. Thesesplit laser beams are converged into 1 beam at an irradiated surface1011 by cylindrical lenses 10091 and 10101.

[0060] On the other hand, the third harmonic is first split into 2 beamsin the vertical direction by cylindrical lens array 10072, and thensplit into 2 beams in the horizontal direction by a cylindrical lensarray 10082. These split beams are converged into 1 beam at theirradiated surface 1011 by cylindrical lenses 10092 and 10102.

[0061] The reason why the structure of FIG. 10 is able to make theinterference pattern become inconspicuous will be explained withreference to FIG. 11. FIG. 11 is a top view of the optical system ofFIG. 10. The laser beam split into 4 laser beams and converged into 1beam in the longitudinal direction of the linear laser beam are denotedby the following names, respectively: laser beam A (the laser beam thatpasses the outermost right-hand side), laser beam B (the laser beam thatpasses the inner side of the right-hand side), laser beam C (the laserbeam that passes the inner side of the left-hand side), and laser D (thelaser beam that passes the outermost left-hand side).

[0062] Laser beam A is the third harmonic and laser beam D is the secondharmonic. Both laser beams are advancing in opposite directions fromeach other at equivalent speeds, and therefore the effect of making theinterference pattern in the irradiated surface 1011 inconspicuous isattained. Laser beam B is the third harmonic and laser beam C is thesecond harmonic. Both laser beams are advancing in opposite directionsfrom each other at equivalent speeds, thereby attaining the effect ofmaking the interference pattern in the irradiated surface 1011inconspicuous. That is, laser beam A and laser beam D erase aninterference effect with each other. Furthermore, laser beam B and laserbeam C erase an interference effect with each other.

[0063] Shown in FIG. 12A is the state of an interference in theirradiated surface 1011, which is calculated by a computer, when thelaser beams in FIG. 11 are all second harmonic. In this graph, it isapparent that the formation of loops and nodes are distinctive due tothe influence of interference. On the other hand, shown in FIG. 12B isthe state of an interference in the irradiated surface 1011 when theabove method is adopted in the optical system of FIG. 11. The loops andnodes that were seen in FIG. 12A have disappeared, and hence it isdiscerned that the energy has been made uniform. The essence of thepresent invention is in making each of the lights having differentwavelengths uniform and then synthesizing the respective uniform lightsinto 1 light in the irradiated surface.

[0064] Accordingly, the possible stripe pattern developing in thesemiconductor film when the semiconductor film is laser annealed with aYAG laser that has been processed into a linear laser beam can thus bemade unnoticeable. Although cited in the present specification is anexample of taking out laser beams having different wavelengths from eachother from 1 laser oscillator, there is no influence of any kindinflicted upon the essence of the present invention even if laser beamshaving different wavelengths from each other are taken out from 2 laseroscillators. In this case, a trigger is tuned in to so that the emissionof lasers having different wavelengths from each other may be performedat the same time. The present invention is not limited to the YAG laserbut can be applied to all laser irradiation apparatuses having a longcoherent length such as a glass laser and an Ar laser. In addition, thepresent invention is not limited to a linear laser beam that has alinear section in the irradiated surface but is also applicable to arectangular laser beam having a small aspect ratio. The presentinvention is further applicable to a square shape laser beam.

[0065] That is, according to the present invention, there is provided alaser irradiation apparatus that irradiates a laser beam with a sectionwhich becomes linear, square-like, or rectangular in an irradiatedsurface, characterized by comprising a laser oscillator that emits aplurality of laser beams having different wavelengths from each other,an optical system for processing the plurality of sectional laser beamshaving different wavelengths from each other into a square-like orrectangular laser beam in the irradiated surface, respectively, andmaking an energy distribution uniform, and a stage for arranging anobject to be irradiated.

[0066] According to another aspect of the present invention, there isprovided a laser irradiation apparatus that irradiates a laser beam witha section which becomes linear in an irradiated surface, characterizedby comprising a laser oscillator that emits a plurality of laser beamshaving different wavelengths from each other, an optical system forprocessing the plurality of sectional laser beams having differentwavelengths from each other into a linear laser beam in the irradiatedsurface, respectively, and making an energy distribution uniform, and ameans of relatively moving the object to be irradiated to the laserbeam.

[0067] In any of the above-mentioned inventions, since the laseroscillator is a YAG laser and the maintenance of the laser apparatus iseasy to manage, productivity is increased and is thus preferable.Further, the YAG laser is capable of generating harmonics readily, andhence is suitable for use in the present invention.

[0068] Also, in any of the above-mentioned inventions when the object tobe irradiated is a non-single crystal silicon film, laser beams having awavelength of 600 nm or less may be used as the laser beams havingdifferent wavelengths from each other because the processing efficiencyis high. For example, it is good to use the combination the secondharmonic and the third harmonic of the YAG laser, or the combination thesecond harmonic and the fourth harmonic of the YAG laser, or thecombination the third harmonic and the fourth harmonic of the YAG laserbecause the processing efficiency is high. Other than the YAG laser, aYVO4 laser, a glass laser, etc. can be used in the present invention.

[0069] Both of the above-mentioned laser apparatuses have a load/unloadchamber, a transfer chamber, a pre-heat chamber, a laser irradiationchamber, and a cooling chamber. Both laser apparatuses are preferred forthey can be used in mass production.

[0070] Further, according to another aspect of the present invention,there is provided a laser irradiation method that simultaneouslyirradiates each of a plurality of laser beams having differentwavelengths from each other to a same region, characterized in that theshape of the laser beam in the same region is square-like orrectangular.

[0071] Further, according to another aspect of the present invention,there is provided a laser irradiation method that simultaneouslyirradiates each of a plurality of laser beams having differentwavelengths from each other to a same region, characterized in that theshape of the laser beam in the same region is linear.

[0072] Further, according to another aspect of the present invention,there is provided a laser irradiation method that simultaneouslyirradiates each of a plurality of laser beams having differentwavelengths from each other to a same region of a substrate having anon-single crystal semiconductor film formed thereon, characterized inthat the shape of the laser beam in the same region is square-like orrectangular.

[0073] Further, according to another aspect of the present invention,there is provided a laser irradiation method that simultaneouslyirradiates each of a plurality of laser beams having differentwavelengths from each other to a same region of a substrate having anon-single crystal semiconductor film formed thereon, characterized inthat the shape of the laser beam in the same-region is linear and thatthe linear laser beam is irradiated to the non-single crystalsemiconductor film while relatively scanning the linear laser beam tothe non-single crystal semiconductor film.

[0074] Still further, according to another aspect of the presentinvention, there is provided a method of manufacturing a semiconductordevice provided with a TFT formed on a substrate, characterized bycomprising the steps of forming a non-single crystal semiconductor filmon the substrate and simultaneously irradiating a plurality of laserbeams having different wavelengths from each other to a certain regionof the non-single crystal semiconductor film.

[0075] Still further, according to another aspect of the presentinvention, there is provided a method of manufacturing a semiconductordevice provided with a TFT formed on a substrate, characterized bycomprising the steps of forming a non-single crystal semiconductor filmon the substrate and simultaneously irradiating a plurality of laserbeams having different wavelengths from each other to a region of thenon-single crystal semiconductor film to thereby transform thenon-single crystal semiconductor film into a crystalline semiconductorfilm.

[0076] In any one of the above-mentioned inventions, the laser beam is aYAG laser and the maintenance of the laser apparatus can be easilymanaged, and therefore the inventions thereof are appreciated. Also,because the plurality of laser beams having different wavelengths fromeach other have a wavelength of 600 nm or less in any one of theabove-mentioned inventions, their absorption to the semiconductor filmis large and hence the inventions thereof are appreciated. As laserbeams having a wavelength of 600 nm or less, there are, for example, thesecond harmonic, the third harmonic, and the fourth harmonic of the YAGlaser.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The above and other objects and features of the present inventionwill become more apparent from the following description taken inconjunction with the accompanying drawings:

[0078]FIGS. 1A and 1B are diagrams showing a side view and a top view,respectively, of a conventional optical system that forms a linear laserbeam;

[0079]FIG. 2 is a view illustrating the structure of a YAG laser of azigzag slub system;

[0080]FIG. 3A is a view showing an energy distribution of a linear laserbeam and FIG. 3B is a view showing the state of a silicon filmirradiated with a linear laser beam while the linear laser beam isscanned in a direction at a right angle in the longitudinal directionthereof;

[0081]FIG. 4A is a view showing an example of an optical systemprocessing a second harmonic of a YAG laser into a linear laser beam byusing a beam homogenizer, and FIG. 4B is a view illustrating a profileof an interference caused by the second harmonic of the YAG laser whichis processed into a linear laser beam by using the beam homogenizer;

[0082]FIG. 5A is a view showing an example of an optical system using abeam homogenizer to synthesize a second harmonic and a third harmonic ofa YAG laser to thereby form a linear laser beam, and FIG. 5B is viewillustrating a profile of an interference caused by the second harmonicand the third harmonic of the YAG laser which are synthesized andprocessed into a linear laser beam by using the beam homogenizer;

[0083]FIG. 6 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

[0084]FIG. 7 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

[0085]FIG. 8 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

[0086]FIG. 9 is a view illustrating a calculation result of an energyintensity distribution of a light interference;

[0087]FIG. 10 is a diagram showing an example of a laser irradiationapparatus disclosed in the present invention;

[0088]FIG. 11 is a diagram showing an example of a laser irradiationapparatus disclosed in the present invention;

[0089]FIGS. 12A and 12B are views illustrating a calculation result ofan energy intensity distribution of a light interference;

[0090]FIG. 13 is a diagram showing an example of a laser irradiationapparatus disclosed in the present invention;

[0091]FIG. 14 is a diagram showing a laser irradiation apparatus formass production;

[0092]FIGS. 15A to 15D are diagrams showing an example of amanufacturing process of the present invention;

[0093]FIGS. 16A to 16D are diagrams showing an example of amanufacturing process of the present invention;

[0094]FIGS. 17A to 17D are diagrams showing an example of amanufacturing process of the present invention;

[0095]FIGS. 18A to 18C are diagrams showing an example of amanufacturing process of the present invention;

[0096]FIG. 19 is a diagram showing an example of a manufacturing processof the present invention;

[0097]FIG. 20 is a diagram showing a top view of a pixel;

[0098]FIG. 21 is a diagram showing the cross-sectional structure of aliquid crystal display device;

[0099]FIGS. 22A to 22C are diagrams showing an example of amanufacturing process of the present invention;

[0100]FIGS. 23A to 23D are diagrams showing an example of amanufacturing process of the present invention;

[0101]FIG. 24 is a diagram showing the outer appearance of an AM-LCD;

[0102]FIGS. 25A and 25B are diagrams showing the structure of an activematrix type EL display device;

[0103]FIGS. 26A and 26B are diagrams showing the structure of an activematrix type EL display device;

[0104]FIG. 27 is a diagram showing the structure of an active matrixtype EL display device;

[0105]FIGS. 28A and 28B are diagrams showing the structure of an activematrix type EL display device;

[0106]FIG. 29 is a diagram showing the structure of an active matrixtype EL display device;

[0107]FIGS. 30A to 30C are diagrams showing a circuit configuration ofan active matrix type EL display device;

[0108]FIGS. 31A to 31F are diagrams showing examples of an electronicdevice;

[0109]FIGS. 32A to 32D are diagrams showing examples of an electronicdevice;

[0110]FIGS. 33A to 33C are diagrams showing examples of an electronicdevice; and

[0111]FIG. 34 is a graph illustrating a wavelength dependence of a ratioof the absorption of light to a 55 nm-thick a-Si film formed on a glasssubstrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode of the PresentInvention

[0112] First, an example of irradiating a laser beam, which has beenprocessed into a linear laser beam at an irradiated surface, to a 5 inchsquare substrate having an a-Si film formed thereon as an object to beirradiates is shown.

[0113] A 0.7-thick Corning 1737 is used as the substrate. If the Corning1737 substrate has sufficient durability up to a temperature of 600° C.An SiO₂ film is formed to a thickness of 200 nm on one side of thesubstrate by plasma CVD. Further, a 55 nm-thick a-Si film is formedthereon. As the film deposition method, for example, sputtering or thelike may be used.

[0114] The substrate, completed with the formation of the silicon films,is exposed in a nitrogen atmosphere at a temperature of 500° C. for 1hour to thereby reduce the hydrogen concentration in the a-Si film. Thelaser resistance of the a-Si film can thus be enhanced. An appropriateconcentration of hydrogen inside the a-Si film is on the order of 10²⁰atoms/cm³. The formation of the object to be irradiated is thuscompleted. Then laser is irradiated to the object to thereby performcrystallization of the a-Si film.

[0115] Before performing laser irradiation to the a-Si film, heat may beapplied thereto to perform crystallization. For example, the a-Si filmmay be crystallized by adding therein an element that promotescrystallization and then performing heat treatment. The detailsregarding the method of crystallizing the a-Si film by adding therein anelement that promotes crystallization and then applying heat isexplained in Embodiment 1.

[0116]FIG. 13 is a view illustrating a laser irradiation apparatus. Thelaser irradiation apparatus shown in FIG. 13 is one example of anapparatus that irradiates a linear laser beam to a substrate. Thestructure thereof is the same as the optical system shown in FIG. 1. Alaser beam is processed into a 115 mm long and 0.5 mm wide linear laserbeam by the optical system shown in FIG. 13. Because the length of thelinear laser beam is 115 mm, it is scanned in one direction to the 5inch square (about 125 mm) substrate, whereby almost the entire surfaceof the substrate can be irradiated with the laser beam. The opticalsystem illustrated in FIG. 13 is one example thereof. The linear laserbeam is imaged on the a-Si film. The size of the above-mentioned linearlaser beam is the size of the beam when imaged on the a-Si film. Thestructure of the optical system is explained in the following. A pulseoscillation type YAG laser oscillator 1301 oscillates a laser beamhaving a fundamental wave (wavelength of 1065 nm), a second harmonic(wavelength of 533 nm), and a third harmonic (wavelength of 355 nm). Theabove-mentioned YAG laser is a zigzag slub system YAG laser. The sizesof the above laser beams at the exit of the respective laser beams are6×12 mm and rectangular in shape. Further, the largest outputs of thelaser beams are 800 mJ/pulse at the second harmonic and 400 mJ/pulse atthe third harmonic. A largest repetitive frequency is 30 Hz and a pulsewidth is 10 ns.

[0117] From the fact that the 533 nm laser beam and the 355 nm laserbeam having different wavelengths from each other are used, a syntheticquartz that has a high transmittance at the wavelength region thereof isused as the core of the lenses. Because laser beams having differentwavelengths from each other are passed through the optical system, theradius of curvature of the lenses that the second harmonic penetratesand the radius of the curvature of the lenses that the third harmonicpenetrates must be changed even if, for example, the focal lengthsthereof are equivalent. Further, a coating that is appropriate for eachof the wavelengths may be applied to the lenses in order to prevent thesurfaces of the lenses from reflecting and to enhance the transmittance.In addition, the life of the lenses can be extended by applying acoating. Depending on the layout of the laser irradiation apparatus, itis necessary to arrange mirrors in appropriate positions. Progress isbeing made in a technique for making mirrors to have a high reflectanceto a very wide range of wavelengths. There are mirrors in which nearly99% or more reflectance can be obtained from both the 355 nm wavelengthand the 533 nm wavelength. Of course, different coatings may be used inaccordance with different wavelengths because a higher reflectance canbe obtained.

[0118] The fundamental wave generated from a resonator 1302 of the YAGlaser is converted into the second harmonic and the third harmonic by anon-linear optical element 1303. Because components of the fundamentalwave still remain in the laser beam, the components thereof areseparated from that of the second harmonic and the third harmonic by abeam splitter 1304 that is arranged at a 45 degree angle to theadvancing direction of the laser beam. The laser beam that istransmitted from the beam splitter 1304 is the fundamental wave and thelaser beam that is reflected is the second harmonic and the thirdharmonic.

[0119] The second harmonic and the third harmonic are separated by abeam splitter 1305 that is arranged at a 45 degree angle to theadvancing direction of the second harmonic and the third harmonic. Thelaser beam that is reflected by the beam splitter 1305 is the secondharmonic and the laser beam that transmitted thereby is the thirdharmonic. Next, the light path of the third harmonic is bend 90 degreesupward by a mirror 1306 and then further bend 90 degrees in a horizontaldirection by a mirror 1307. Thus, the advancing direction of the thirdharmonic is converted into a direction that is the same as the advancingdirection of the second harmonic. At this point, the fundamental wave,the second harmonic, and the third harmonic are simultaneously outputtedat the exit of the laser beam, respectively. A positional relationshipof the laser beams of the second harmonic and the third harmonic is setso that the diagonal line of the rectangular laser beam is on top of thesame linear line.

[0120] The second harmonic separated by the beam splitter 1305 is oncesplit into 2 beams by a cylindrical lens array 13082. Thereafter, thesplit beam is converged into 1 beam at an irradiated surface 1313 by acylindrical lens 13102 and a cylindrical lens 13121. The cylindricallens 13102 and the cylindrical lens 13121 have the shape of acylindrical lens after it has been separated into 2 congruent solidcylindrical lenses at a plane containing a straight line that is calledthe main line (mother line) of a normal cylindrical lens. Such lensesare called half cylindrical lenses throughout the present specification.

[0121] The second harmonic that has been split into 4 beams by acylindrical lens array 13092 is converged into 1 beam at the irradiatedsurface 1313 by a cylindrical lens 13111.

[0122] A coating is applied on the cylindrical lens array 13082, thecylindrical lens array 13092, the cylindrical lens 13102, thecylindrical lens 13111, and the cylindrical lens 13121, respectively, inorder to make the transmittance of the 533 nm wavelength second harmonicto 99% or more.

[0123] On the other hand, the third harmonic reflected by the mirror1307 is once split into 2 beams by a cylindrical lens array 13081.Thereafter, the split beam is converged into 1 beam at the irradiatedsurface 1313 by a cylindrical lens 13101 and a cylindrical lens 13122.The cylindrical lens 13101 and the cylindrical lens 13122 are halfcylindrical lenses.

[0124] The third harmonic that has been further split into 4 beams by acylindrical lens array 13091 is converged into 1 beam at the irradiatedsurface 1313 by a cylindrical lens 13112.

[0125] A coating is applied on the cylindrical lens array 13081, thecylindrical lens array 13091, the cylindrical lens 13101, thecylindrical lens 13112, and the cylindrical lens 13122, respectively, inorder to make the transmittance of the 355 nm wavelength third harmonicto 99% or more.

[0126] Examples of specific sizes and focal lengths of the opticalsystem illustrated in FIG. 13 are shown here in the following. Thelenses shown herein below are all cylindrical lenses and have a radiusof curvature in the width direction.

[0127] First, the structure of the optical system which processes thesecond harmonic is described. The cylindrical lens array 13082 is madeup of 2 cylindrical lenses that are 3 mm wide, 25 mm long, 3 mm thickwith a focal length of 300 mm and combined with each other in the widthdirection in the form of an array.

[0128] The above-mentioned cylindrical lens is a planoconvex lens havinga spherical convex surface. Throughout the present specification, theincident surfaces of the lenses are spherical and the other surfaces areplanar unless particularly stated. To make the lenses into an arrayform, a method that may be used is by adhering them together by applyingheat or fitting the lenses into a frame and then fixing them from theoutside. In addition, the cylindrical lens arrays may be formed into oneunit of cylindrical lens array at the grinding stage.

[0129] The cylindrical lens array 13092 is made up of 4 cylindricallenses that are 3 mm wide, 30 mm long, 3 mm thick with a focal length of25 mm, and combined with each other in the width direction in the formof an array.

[0130] The cylindrical lens 13102 is a half cylindrical lens that is 30mm wide, 80 mm long, 8 mm thick, and has a focal length of 300 mm.

[0131] The cylindrical lens 13111 is a cylindrical lens that is 150 mmwide, 40 mm long, 15 mm thick, and has a focal length of 1000 mm.

[0132] The cylindrical lens 13121 is a half cylindrical lens that is 40mm wide, 150 mm long, and 15 mm thick with a focal length of 175 mm. Inorder to enhance the uniformity of the linear laser beam at theirradiated surface 1313, it is better that the cylindrical lens 13121 isa non-spherical lens. If non-spherical lenses are hard to process, thenit is better to use a set lens such as, for example, a doublet lens or atriplet lens to thereby suppress the spherical aberrations.

[0133] Next, the structure of the optical system which processes thethird harmonic is described. The cylindrical lens array 13081 is made upof 2 cylindrical lenses that are 3 mm wide, 25 mm long, 3 mm thick witha focal length of 300 mm and combined with each other in the widthdirection in the form of an array.

[0134] The cylindrical lens array 13091 is made up of 4 cylindricallenses that are 3 mm wide, 30 mm long, 3 mm thick with a focal length of25 mm, and combined with each other in the width direction in the formof an array.

[0135] The cylindrical lens 13101 is a half cylindrical lens that is 30mm wide, 80 mm long, 8 mm thick, and has a focal length of 300 mm,

[0136] The cylindrical lens 13112 is a cylindrical lens that is 150 mmwide, 40 mm long, 15 mm thick, and has a focal length of 1000 mm.

[0137] The cylindrical lens 13122 is a half cylindrical lens that is 40mm wide, 150 mm long, and 15 mm thick with a focal length of 175 mm. Inorder to enhance the uniformity of the linear laser beam at theirradiated surface 1313, it is better that the cylindrical lens 13122 isa non-spherical lens. If non-spherical lenses are hard to process, thenit is better to use a set lens such as, for example, a doublet lens or atriplet lens to thereby suppress the spherical aberrations.

[0138] Note that for the purpose of protecting the optical system, theatmosphere around the optical system may contain a gas, such asnitrogen, that does not easily react to the lens coating substance.Therefore, the optical system may be enclosed in an optical systemprotection chamber. Using quartz, which has been applied with a coatingin accordance to the respective wavelengths, for a window where a laserenters and exits the optical system protection chamber is good because ahigh transmittance of 99% or more can thus be obtained.

[0139] The substrate having the a-Si film formed thereon is placed onthe irradiated surface 1313 where a stage (not shown), is moved at aconstant speed by using a moving mechanism (not shown), in thelongitudinal direction and the right angle direction of the linear laserbeam (the direction indicated by an arrow) while irradiating the laserbeam. Thus, the laser beam can be irradiated on the entire surface ofthe substrate. A ball screw type, a linear motor, or the like can beused as the moving mechanism.

[0140] The irradiation conditions may be determined within the range ofthe following standards.

[0141] Energy density of a linear laser beam: 50 to 500 mJ/cm²

[0142] Moving speed of the stage: 0.1 to 2 mm/s

[0143] Oscillation frequency of a laser oscillator: 30 Hz

[0144] The above stated irradiation conditions change in accordance withthe pulse width of the laser oscillator, the state of the semiconductorfilm, and the specification of the device to be manufactured. Animplementor will have to determine the details of the conditionsappropriately. Furthermore, the value of the frequency of the laseroscillator is set to a value which is considered to be the highest valueamong the large output YAG lasers sold in the current market. If laserswith a higher frequency are developed in the future, it is suitable toadopt the higher frequency as much as possible in order to improvethroughput. However, if attempts are made to obtain a higher frequencyat the present level, the quality of the laser beam becomes very poor.That is, M² becomes poor, and,therefore it is better to use a frequencyof about 30 Hz.

[0145] The atmosphere during the irradiation of the laser beam is set tothe atmosphere of a clean room. For example, the atmosphere of the cleanroom is air at a temperature of 23° C. As other replacements of theatmosphere, a chamber may be provided and air may be replaced by H₂.Replacements of the atmosphere are performed to prevent contamination ofthe substrate and to prevent the surface of the semiconductor film frombecoming rough. Gas is supplied through a gas cylinder. Theabove-mentioned atmosphere may be H₂, He, N₂, or Ar or a gaseous mixturethereof. In addition, making the atmosphere into a vacuum (10⁻¹ torr orless) also has the contamination prevention effect and the effect ofpreventing the surface from becoming rough.

[0146] Besides using the Corning 1737 as the substrate, the Corning 7059and a glass substrate such as the AN100 can be used, or a quartzsubstrate may be used.

[0147] During the irradiation of the laser beam, when a spot of thesubstrate irradiated with the linear laser beam is heated by applying astrong light using an infrared lamp or the like, the energy of the laserbeam can be reduced compared with the case of not heating the spot ofthe substrate. Heat may also be applied by placing a heater at a bottomportion of the substrate. When the linear laser beam is made longer sothat it may be used for a larger area substrate, the aid of energy dueto the application of heat is useful when the energy of the laser beamis insufficient.

[0148] The laser irradiation apparatus of the present invention isapplicable not only to the non-single crystal silicon film, but also toother non-single crystal semiconductor films such as, for example, anon-single crystal semiconductor film of a diamond or germanium.

[0149] Employing the semiconductor film crystallized by theabove-mentioned laser irradiation apparatus, a semiconductor device suchas a liquid crystal display of a low temperature poly-silicon TFT may bemanufactured by a known method, or a semiconductor device contrived byan implementor may be manufactured.

Embodiment 1

[0150] In the present embodiment, an example will be described in whicha polycrystalline silicon film is irradiated with a laser beam. Thelaser irradiation device described in the above embodiment mode is used.

[0151] A Corning glass 1737 having a thickness of 0.7 mm is used as asubstrate. The substrate has sufficient durability if it is used under600° C. An SiO₂ film is formed in 200 nm on one surface of the substrateby a plasma CVD method. Further, an a-Si film is formed in 55 nm on theSiO₂ film. Any other film forming method, for example, a sputteringmethod may be used.

[0152] Next, the above-mentioned a-Si film is crystallized by the methoddisclosed in Japanese Patent Laid-Open No. 7-130652. The method will bedescribed briefly in the following. The above a-Si film is coated with anickel acetate water solution having a concentration of 10 ppm and thenis heated in a nitrogen atmosphere at 550° C. for 4 hours, whereby thea-Si film is crystallized. It is recommended that a spin coat method,for example, be used for applying the nickel acetate water solution. Thea-Si film to which nickel is added is crystallized in a short period atlow temperatures. It is thought that this is because the nickel acts asthe seed crystal of crystal growth to facilitate the crystal growth.

[0153] If the polycrystalline silicon film crystallized by the abovemethod is irradiated with the laser beam, it has higher characteristicsas a material of a semiconductor element. Accordingly, to improve thecharacteristics of the above polycrystalline silicon film, the abovepolycrystalline silicon film is irradiated with the laser beam by usingthe laser irradiation device used in the embodiment mode of the presentinvention.

[0154] It is recommended that a semiconductor device, for example, aliquid crystal display made of low-temperature polysilicon TFTs, ismanufactured by using a semiconductor film crystallized with the abovelaser irradiation device by a publicly known method. Or a semiconductordevice invented by a practicing person can be manufactured. Theembodiment mode of the present invention and the embodiment 1 can beused in combination.

[0155] Embodiment 2

[0156] Shown in Embodiment 2 is an example of linearly synthesizing thesecond harmonic and the fourth harmonic of the YAG laser at theirradiated surface as the light source of the laser beam.

[0157] The advantages of using the second harmonic are that a largeoutput can be obtained, and further, the optical lenses do notdeteriorate easily. By mixing the fourth harmonic with the secondharmonic, the influence of interference in the irradiated surface canthus be remarkably reduced.

[0158] A method of Embodiment 2 is that a non-linear optical elementwhich forms the second harmonic and the fourth harmonic at the same timeis used instead of the non-linear optical element used in the EmbodimentMode of the present invention. Furthermore, a similar optical system forprocessing the fourth harmonic is used in place of the portion of theoptical system, which processes the third harmonic. The fourth harmonicmay be entered into the optical system.

[0159] Embodiment 2 can be combined with Embodiment 1.

[0160] Embodiment 3

[0161] Shown in Embodiment 3 is an example of linearly synthesizing thethird harmonic and the fourth harmonic of the YAG laser at theirradiated surface as the light source of the laser beam.

[0162] The advantage of using the third harmonic and the fourth harmonicis that both laser beams have an extremely high absorption coefficientwith respect to silicon films. By mixing the fourth harmonic with thethird harmonic, the influence of interference in the irradiated surfacecan thus be remarkably reduced.

[0163] A method of Embodiment 3 is that a non-linear optical elementwhich forms the third harmonic and the fourth harmonic at the same timeis used instead of the non-linear optical element used in the EmbodimentMode of the present invention. Furthermore, a similar optical system forprocessing the fourth harmonic is used in place of the portion of theoptical system, which processes the second harmonic. The fourth harmonicmay be entered into the optical system.

[0164] Embodiment 3 can be combined with Embodiment 1.

[0165] Embodiment 4

[0166] In the present embodiment, an example of a laser irradiationdevice for mass production will be described with reference to FIG. 14.FIG. 14 is a top view of a laser irradiation device.

[0167] A substrate is carried from a load/unload chamber 1401 by the useof a carrying robot arm 1403 mounted in a transfer chamber 1402. First,the substrate is aligned in an alignment chamber 1404 and then iscarried to a pre-heat chamber 1405. In the pre-heat chamber 1405, thesubstrate is previously heated to a desired temperature of about 300°C., for example, by the use of an infrared lamp heater. Then, thesubstrate is placed in a laser irradiation chamber 1407 via a gate valve1406 and then the gate valve 1406 is closed.

[0168] A laser beam is emitted by the laser oscillator 1400 described inthe embodiment mode and then is bent downward 90 degrees by a mirror(not shown) placed directly above a quartz window 1410 via an opticalsystem 1409 and is transformed into a linear laser beam at an irradiatesurface in the laser irradiation chamber 1407 via the quartz window1410. The laser beam is applied to the substrate placed at the irradiatesurface. It is recommended that the above-mentioned optical system beused as the optical system 1409, or the one similar to the opticalsystem may be used. It is preferable to use excimer grade quartz window.The excimer grade quartz window can be used at a state of non-coat,because it has sufficiently transmittance against the second harmonicand the third harmonic.

[0169] The laser irradiation chamber 1407 is evacuated by a vacuum pump1411 to make the atmosphere of the chamber 1407 a high vacuum of about10⁻3 Pa before the irradiation of the laser beam, or the atmosphere ofthe laser irradiation chamber 1407 is made a desired atmosphere by thevacuum pump 1411 and a gas cylinder 1412. As described above, the aboveatmosphere may be He, Ar, H₂, or the mixed gas of them.

[0170] Then, the substrate is scanned and irradiated with the linearlaser beam moved by a moving mechanism 1413. At this time, an infraredlamp (not shown) may be applied to the spot of the substrate irradiatedwith the linear laser beam.

[0171] After the end of the irradiation of the laser beam, the substrateis carried to a cooling chamber 1408 to be allowed to cool slowly andthen is returned to the load/unload chamber 1401 via the alignmentchamber 1404. In this manner, many substrates can be annealed with laserby repeating these actions.

[0172] The embodiment 4 can be used in combination with the embodimentmode and the other embodiments of the present invention.

[0173] Embodiment 5

[0174] The present embodiment is described by using FIGS. 15 to 21.Here, the method of fabricating pixel TFTs for the display region andTFTs of driving circuits provided in the periphery of the displayregion, over a same substrate, and a display device manufactured byusing it will be described in detail in accordance with the fabricatingsteps. However, in order to simplify the description, CMOS circuits thatare the basic circuits of a shift register circuit, a buffer circuit,and the like for the control circuit and n-channel type TFTs that formsampling circuits will be shown in the figures.

[0175] In FIG. 15A, a low-alkaline glass substrate or a quartz substratecan be used as a substrate 1501. In this embodiment, a low-alkalineglass substrate was used. On the surface of this substrate 1501 on whichTFTs are to be formed, a base film 1502 such as a silicon oxide film, asilicon nitride film or a silicon oxynitride film is formed in order toprevent the diffusion of impurities from the substrate 1501. Forexample, a silicon oxynitride film which is fabricated from SiH₄, NH₃,N₂O by plasma CVD into 100 nm and a silicon oxynitride film which issimilarly fabricated from SiH₄ and N₂ 0 into 200 nm are formed into alaminate.

[0176] Next, a semiconductor film 1503 a that has an amorphous structureand a thickness of 20 to 150 nm (preferably, 30 to 80 nm) is formed by aknown method such as plasma CVD or sputtering. In this embodiment, anamorphous silicon film was formed to a thickness of 55 nm by plasma CVD.As semiconductor films which have an amorphous structure, there are anamorphous semiconductor film and a microcrystalline semiconductor film;and a compound semiconductor film with an amorphous structure such as anamorphous silicon germanium film may also be applied. Further, the basefilm 1502 and the amorphous silicon film 1503 a can be formed by thesame deposition method, so that the two films can be formed insuccession. By not exposing the base film to the atmospheric air afterthe formation of the base film, the surface of the base film can beprevented from being contaminated, as a result of which the dispersionin characteristics of the fabricated TFTs and the variation in thethreshold voltage thereof can be reduced. (FIG. 15A)

[0177] Then, by a known crystallization technique, a crystalline siliconfilm 1503 b is formed from the amorphous silicon film 1503 a. In thepresent embodiment, laser crystallization was performed in accordancewith the above stated embodiment mode by using a laser apparatus of thepresent invention. It is preferred that, prior to the crystallizationstep, heat treatment is carried out at 400 to 500° C. for about one hourthough it depends on the amount of hydrogen contained, so that, afterthe amount of hydrogen contained is reduced to 5 atom % or less, thecrystallization is carried out. (FIG. 15B)

[0178] Then, the crystalline silicon film 1503 b is divided intoislands, to form island semiconductor layers 1504 to 1507. Thereafter, amask layer 1508 of a silicon oxide film is formed to a thickness of 50to 100 nm by plasma CVD or sputtering. (FIG. 15C)

[0179] Then, a resist mask 1509 is provided, and, into the wholesurfaces of the island semiconductor layers 1505 to 1507 forming then-channel type TFTs, boron (B) was added as an impurity elementimparting p- type conductivity, at a concentration of about 1×10¹⁶ to5×10¹⁷ atoms/cm³, for the purpose of controlling the threshold voltage.The addition of boron (B) may be performed either by the ion doping orit may be added simultaneously when the amorphous silicon film isformed. The addition of boron (B) here was not always necessary,however, the formation of semiconductor layers 1510 to 1512 into whichboron was added was preferable for maintaining the threshold voltage ofthe n-channel type TFTs within a prescribed range. (FIG. 15D)

[0180] In order to form the LDD regions of the n-channel type TFTs inthe driving circuit, an impurity element imparting n-type conductivityis selectively added to the island semiconductor layers 1510 and 1511.For this purpose, resist masks 1513 to 1516 were formed in advance. Asthe impurity element imparting the n-type conductivity, phosphorus (P)or arsenic (As) may be used; here, in order to add phosphorus (P), iondoping using phosphine (PH₃) was applied. The concentration ofphosphorus (P) in the impurity regions 1517 and 1518 thus formed may beset within the range of from 2×10¹⁶ to 5×10¹⁹ atoms/cm³. In thisspecification, the concentration of the impurity element contained inthe thus formed impurity regions 1517 to 1519 imparting n-typeconductivity is represented by (n⁻). Further, the impurity region 1519is a semiconductor layer for forming the storage capacitor of the pixelmatrix circuit; into this region, phosphorus (P) was also added at thesame concentration. (FIG. 16A)

[0181] Next, the mask layer 1508 is removed by hydrofluoric acid or thelike, and the step of activating the impurity elements added at thesteps shown in FIG. 15D and FIG. 16A is carried out. The activation canbe carried out by performing heat treatment in a nitrogen atmosphere at500 to 600° C. for 1 to 4 hours or by using the laser activation method.Further, both methods may be jointly performed. Or, the laserirradiation described in the embodiment mode may be performed. In thisembodiment, the laser activation method was employed, and a KrF excimerlaser beam (with a wavelength of 248 nm) was used; the beam is formedinto a linear beam; and scan was carried out under the condition thatthe oscillation frequency was 5 to 50 Hz, the energy density was 100 to500 mJ/cm², and the overlap ratio of the linear beam was 80 to 98%,whereby the whole substrate surface on which the island semiconductorlayers were formed was processed. Any item of the laser irradiationcondition is subjected to no limitation, so that the operator maysuitably select the condition.

[0182] Then, a gate insulating film 1520 is formed of an insulating filmcomprising silicon to a thickness of 10 to 150 nm, by plasma CVD orsputtering. For example, a silicon oxynitride film is formed to athickness of 120 nm. As the gate insulating film, other insulating filmscomprising silicon may be used as a single layer or a laminatestructure. (FIG. 16B)

[0183] Next, in order to form a gate electrode, a first conductive layeris deposited. This first conductive layer may be formed of a singlelayer but may also be formed of a laminate consisting of two or threelayers. In this embodiment, a conductive layer (A) 1521 comprising aconductive metal nitride film and a conductive layer (B) 1522 comprisinga metal film are laminated. The conductive layer (B) 1522 may be formedof an element selected from among tantalum (Ta), titanium (Ti),molybdenum (Mo) and tungsten (W) or an alloy comprised mainly of theabove-mentioned element, or an alloy film (typically, an Mo—W alloy filmor an Mo—Ta alloy film) comprised of a combination of theabove-mentioned elements, while the conductive layer (A) 1521 is formedof a tantalum nitride (TaN) film, a tungsten nitride (WN) film, atitanium nitride (TiN) film, or a molybdenum nitride (MoN) film.Further, as the substitute materials of the conductive film (A) 1521,tungsten silicide, titanium silicide, and molybdenum silicide may alsobe applied. The conductive layer (B) may preferably have its impurityconcentration reduced in order to decrease the resistance thereof; inparticular, as for the oxygen concentration, the concentration may beset to 30 ppm or less. For example, tungsten (W) could result inrealizing a resistivity of 20 μΩcm or less by rendering the oxygenconcentration thereof to 30 ppm or less.

[0184] The conductive layer (A) 1521 may be set to 10 to 50 nm(preferably, 20 to 30 nm), and the conductive layer (B) 1522 may be setto 200 to 400 nm (preferably, 250 to 350 nm). In this embodiment, as theconductive layer (A) 1521, a tantalum nitride film with a thickness of30 nm was used, while, as the conductive layer (B) 1522, a Ta film witha thickness of 350 nm was used, both films being formed by sputtering.In case of performing sputtering here, if a suitable amount of Xe or Kris added into the sputtering gas Ar, the internal stress of the filmformed is alleviated, whereby the film can be prevented from peelingoff. Though not shown, it is effective to form a silicon film, intowhich phosphorus (P) is doped, to a thickness of about 2 to 20 nmunderneath the conductive layer (A) 1521. By doing so, the adhesivenessof the conductive film formed thereon can be enhanced, and at the sametime, oxidation can be prevented. In addition, the alkali metal elementslightly contained in the conductive layer (A) or the conductive layer(B) can be prevented from diffusing into the gate insulating film 1520.(FIG. 16C)

[0185] Next, resist masks 1523 to 1527 are formed, and the conductivelayer (A) 1521 and the conductive layer (B) 1522 are etched together toform gate electrodes 1528 to 1531 and a capacitor wiring 1532. The gateelectrodes 1528 to 1531 and the capacitor wiring 1532 are formed in sucha manner that the layers 1528 a to 1532 a comprised of the conductivelayer (A) and the layers 1528 b to 1532 b comprised of the conductivelayer (B) are respectively formed integrally. In this case, the gateelectrodes 1529 and 1530 formed in the driving circuit are formed so asto overlap the portions of the impurity regions 1517 and 1518 throughthe gate insulating film 1520. (FIG. 16D) Then, in order to form thesource region and the drain region of the p-channel TFT in the drivingcircuit, the step of adding an impurity element imparting p-typeconductivity is carried out. Here, by using the gate electrode 1528 as amask, impurity regions are formed in a self-alignment manner. In thiscase, the region in which the n-channel TFT will be formed is coatedwith a resist mask 1533 in advance. Thus, impurity regions 1534 wereformed by ion doping using diborane (B₂H₆). The concentration of boron(B) in this region is set at 3×10²⁰ to 3×10²¹ atoms/cm³. In thisspecification, the concentration of the impurity element impartingp-type contained in the impurity regions 1534 is represented by (p⁺).(FIG. 17A)

[0186] Next, in the n-channel TFTs, impurity regions that function assource regions or drain regions were formed. Resist masks 1535 to 1537were formed, and impurity regions 1538 to 1542 were formed by adding animpurity element for imparting the n-type conductivity. This was carriedout by ion doping using phosphine (PH₃), and the phosphorus (P)concentration in these regions was set to 1×10²⁰ to 1×10²¹ atoms/cm³. Inthis specification, the concentration of the impurity element impartingthe n-type contained in the impurity regions 1538 to 1542 formed here isrepresented by (n⁺). (FIG. 17B)

[0187] In the impurity regions 1538 to 1542, the phosphorus (P) or boron(B) which was added at the preceding steps are contained, however, ascompared with this impurity element concentration, phosphorus is addedhere at a sufficiently high concentration, so that the influence by thephosphorus (P) or boron (B) added at the preceding steps need not betaken into consideration. Further, the concentration of the phosphorus(P) that is added into the impurity regions 1538 is ½ to ⅓ of theconcentration of the boron (B) added at the step shown in FIG. 17A; andthus, the p-type conductivity was guaranteed, and no influence wasexerted on the characteristics of the TFTs.

[0188] Then, the step of adding an impurity imparting n-type isperformed to form the LDD regions of the n-channel type TFTs in thepixel matrix circuit. Here, by using the gate electrode 1531 as a mask,the impurity element for imparting n-type was added in a self-alignmentmanner. The concentration of phosphorus (P) added was 1×10¹⁶ to 5×10¹⁸atoms/cm³; by thus adding phosphorus at a concentration lower than theconcentrations of the impurity elements added at the steps shown in FIG.16A, FIG. 17A and FIG. 17B, only impurity regions 1543 and 1544 weresubstantially formed. In this specification, the concentration of theimpurity element for imparting the n-type conductivity contained inthese impurity regions 1543 and 1544 is represented by (n⁻⁻). (FIG. 17C)

[0189] Thereafter, in order to activate the impurity elements, whichwere added at their respective concentrations for imparting n-type orp-type conductivity, a heat treatment step was carried out. This stepcan be carried out by furnace annealing, laser annealing or rapidthermal annealing (RTA). Here, the activation step was performed byfurnace annealing. Heat treatment is carried out in a nitrogenatmosphere with an oxygen concentration of 1 ppm or less, preferably 0.1ppm or less, at 400 to 800° C., typically at 500 to 600° C.; in thisembodiment, the heat treatment was carried out at 550° C. for 4 hours.Further, in the case a substrate such as a quartz substrate which hasheat resistance is used as the substrate 1501, the heat treatment may becarried out at 800° C. for one hour; in this case, the activation of theimpurity elements and the junctions between the impurity regions intowhich the impurity element was added and the channel forming regioncould be well formed.

[0190] By this heat treatment, on the metal films 1528 b to 1532 b,which form the gate electrodes 1528 to 1531 and the capacitor wiring1532, conductive layers (C) 1528 c to 1532 c are formed with a thicknessof 5 to 80 nm as measured from the surface. For example, in the case theconductive layers (B) 1528 b to 1532 b are made of tungsten (W),tungsten nitride (WN) is formed; in the case of tantalum (Ta), tantalumnitride (TaN) can be formed. Further, the conductive layers (C) 1528 cto 1532 c can be similarly formed by exposing the gate electrodes 1528to 1531 to a plasma atmosphere containing nitrogen using nitrogen,ammonia or the like. Further, heat treatment was carried out in anatmosphere containing 3 to 100% of hydrogen at 300 to 450° C. for 1 to12 hours, thus performing the step of hydrogenating the islandsemiconductor layers. This step is a step for terminating the danglingbonds of the semiconductor layers by the thermally excited hydrogen. Asanother means for the hydrogenation, plasma hydrogenation (using thehydrogen excited by plasma) may be performed. (FIG. 17D)

[0191] After the activation and hydrogenation steps are over, a secondconductive film is formed as gate wiring. This second conductive film ispreferably formed of a conductive layer (D) comprised mainly of aluminum(Al) or copper (Cu) that is a low resistance material, and a conductivelayer (E) comprised of titanium (Ti), tantalum (Ta), tungsten (W), ormolybdenum (Mo). In this embodiment, the second conductive film wasformed by using, as the conductive layer (D) 1545, an aluminum (Al) filmcontaining 0.1 to 2 wt % of titanium (Ti), and by using a titanium (Ti)film as the conductive layer (E) 1546. The conductive layer (D) 1545 maybe formed to a thickness of 200 to 400 nm (preferably, 250 to 350 nm),while the conductive layer (E) 1546 may be formed to a thickness of 50to 200 nm (preferably, 100 to 150 nm). (FIG. 18A)

[0192] Then, in order to form gate wirings connected to the gateelectrodes, the conductive layer (E) 1546 and the conductive layer (D)1545 were etched, whereby gate wirings 1547, 1548 and a capacitor wiring1549 were formed. The etching treatment was carried out in such a mannerthat, at first, by a dry etching method using a mixture gas of SiCl₄,Cl₂ and BCl₃, the portions extending from the surface of the conductivelayer (E) to a part of the way of the conductive layer (D) were removed,and, thereafter, the conductive layer (D) was removed by wet etchingusing a phosphoric acid etching solution, whereby the gate wirings couldbe formed, maintaining a selective workability with respect to the basefilm.(FIG. 18B)

[0193] A first interlayer insulating film 1550 is formed of a siliconoxide film or a silicon oxynitride film with a thickness of 500 to 1500nm, and contact holes reaching the source regions or the drain regions,which are formed in the respective island semiconductor layers, areformed; and source wirings 1551 to 1554 and drain wirings 1555 to 1558are formed. Though not shown, in this embodiment, these electrodes wereformed from a laminate film of three-layer structure which was formed bysuccessively forming by sputtering: a Ti film to 100 nm; an aluminumfilm containing Ti to 300 nm; and a Ti film to 150 nm.

[0194] Next, as a passivation film 1559, a silicon nitride film, asilicon oxide film or a silicon oxynitride film is formed to a thicknessof 50 to 500 nm (typically 100 to 300 nm). In the case that ahydrogenating treatment was carried out in this state, a preferableresult was obtained in respect of the enhancement in characteristics ofthe TFTs. For example, it is preferable to carry out heat treatment inan atmosphere containing 3 to 100% of hydrogen at 300 to 450° C. for 1to 12 hours; or, in the case that the plasma hydrogenation method wasemployed, a similar effect was obtained. Here, openings may be formed inthe passivation film 1559 at the positions at which contact holes forconnecting the pixel electrodes and drain wirings to each other will beformed later. (FIG. 18C)

[0195] Thereafter, a second interlayer insulating film 1560 comprised ofan organic resin is formed to a thickness of 1.0 to 1.5 μm. As theorganic resin, polyimide, acrylic, polyamide, polyimideamide, or BCB(benzocyclobutene) can be used. Here, the second interlayer film wasformed by using a polyimide of the type which thermally polymerizesafter applied to the substrate, and it was fired at 300° C. Then, acontact hole reaching the drain wiring 1558 was formed in the secondinterlayer insulating film 1560, and pixel electrodes 1561 and 1562 wereformed. The pixel electrodes may use a transparent conductive film inthe case a transmission type liquid crystal display device is to beobtained, while, in the case a reflection type liquid crystal displaydevice is to be fabricated, it may use a metal film. In this embodiment,a transmission type liquid crystal display device is to be fabricated,so that an indium tin oxide (ITO) film was formed to a thickness of 100nm by sputtering. (FIG. 19)

[0196] In this way, a substrate having the TFTs of the driving circuitand the pixel TFTs of the display region on the same substrate could becompleted. In the driving circuit, there were formed a p-channel TFT1601, a first n-channel TFT 1602 and a second n-channel TFT 1603, while,in the display region, there were formed a pixel TFT 1604 and a storagecapacitor 1605. In this specification, such a substrate is called activematrix substrate for convenience.

[0197] Note that FIG. 20 is a top view showing almost one pixel in thedisplay region. The cross section along with A-A′ shown in FIG. 20corresponds to the cross sectional diagram of the display region shownin FIG. 19. Further, common reference numerals are used in FIG. 20 tocorrespond with the cross sectional diagrams of FIGS. 15 to 19. The gatewiring 1548 intersects, by interposing a gate insulating film that isnot shown in the figure, with a semiconductor layer 1507 underneath.Though not shown, a source region, a drain region, and a Loff regionwhich is formed from n⁻⁻ region are formed in the semiconductor layer.Reference numeral 1563 denotes a contact section of the source wiring1554 and the source region 1624; 1564, a contact section of the drainwiring 1558 and the drain region 1626; 1565, a contact section of thedrain wiring 1558 and the pixel electrode 1561. Storage capacitor 1605is formed in the region where a semiconductor layer 1627 extended fromthe drain region 1626 of the pixel TFT 1604 overlap capacitor wirings1532 and 1549 by interposing a gate insulating film.

[0198] The p-channel TFT 1601 in the driving circuit has a channelforming region 1606, source regions 1607 a and 1607 b and drain regions1608 a and 1608 b in the island semiconductor layer 1504. The firstn-channel TFT 1602 has a channel forming region 1609, a LDD region 1610overlapping the gate electrode 1529 (such a LDD region will hereinafterbe referred to as Lov), a source region 1611 and a drain region 1612 inthe island semiconductor layer 1505. The length in the channel directionof this Lov region is set to 0.5 to 3.0 μm, preferably 1.0 to 1.5 μm. Asecond n-channel TFT 1603 has a channel forming region 1613, LDD regions1614 and 1615, a source region 1616 and a drain region 1617 in theisland semiconductor layer 1506. In these LDD regions, there are formedan Lov region and a LDD region which does not overlap the gate electrode1530(such an LDD region will hereafter be referred as Loff); and thelength in the channel direction of this Loff region is 0.3 to 2.0 μm,preferably 0.5 to 1.5 μm. The pixel TFT 1604 has channel forming regions1618 and 1619, Loff regions 1620 to 1623, and source or drain regions1624 to 1626 in the island semiconductor layer 1507. The length in thechannel direction of the Loff regions is 0.5 to 3.0 μm, preferably 1.5to 2.5 μm. Further, the storage capacitor 1605 comprises capacitorwirings 1532 and 1549, an insulating film composed of the same materialas the gate insulating film, and a semiconductor layer 1627 which isconnected to the drain region 1626 of the pixel TFT 1604 and in which animpurity element for imparting the n-type conductivity is added. It isnot necessary to limit the present invention to the structure of thestorage capacitor shown in the present embodiment. For example, storagecapacitors of the structures disclosed in Japanese Patent ApplicationNo. Hei 9-316567, Hei 9-273444 or 10-254097, of the present applicant,can be used.

[0199] In FIG. 19, the pixel TFT 1604 is of the double gate structure,but may be of the single gate structure, or may be of a multi-gatestructure in which a plurality of gate electrodes are provided.

[0200] The processes for manufacturing an active matrix liquid crystaldisplay device from the above stated active matrix substrate isdescribed. As shown in FIG. 21, an alignment film 1701 is formed ontothe active matrix substrate of the state of FIG. 19 manufactured throughthe above stated method. Polyimide resin is used in general for analignment film of a liquid crystal display element. A shielding film1703, a transparent conductive film 1704 and an alignment film 1705 areformed on the opposing substrate 1702 on the opposite side. Afterforming the alignment film, rubbing treatment is performed to make theliquid crystal molecules orient with a constant pre-tilt angle. Theactive matrix substrate formed with the pixel matrix circuit and theCMOS circuits, and the opposing substrate are stuck together by asealant (not shown) or column spacers 1707 through a known cell assemblyprocess. Liquid crystal material 1706 is then injected between thesubstrates and completely sealed by a sealant (not shown). Known liquidcrystal materials can be used for the liquid crystal materials. Anactive matrix liquid crystal display device shown in FIG. 21 is thuscomplete.

[0201] As described above, an active matrix liquid crystal displaydevice in which TFT structures that comprise each circuit are optimizedin accordance with the specification required by the pixel TFT and thedriver circuit, can be formed.

[0202] Note that any constitution of the Embodiments 1 to 12 may be usedin manufacturing a semiconductor device shown in the present embodiment,and it is possible to freely combine each embodiments.

[0203] Embodiment 6

[0204] Referring to FIGS. 22A to 22C, an example of using another methodof crystallization, substituting the crystallization step in Embodiment5, is shown here in Embodiment 6.

[0205] First, the state of FIG. 22A is obtained in accordance withEmbodiment 5. Note that FIG. 22A corresponds to FIG. 15A.

[0206] A catalyst element for promoting crystallization (one or pluralkinds of elements selected from a group consisting of nickel, cobalt,germanium, tin, lead, palladium, iron, and copper, typically nickel) isused for performing crystallization. Specifically, laser crystallizationis performed under a state in which the catalyst element is maintainedin a surface of an amorphous silicon film to transform the amorphoussilicon film into a crystalline silicon film. In Embodiment 6, anaqueous solution containing nickel (aqueous nickel acetate solution) isapplied to the amorphous silicon film by spin coating to form acatalyst-element-containing layer 1801 on the entire surface of anamorphous semiconductor film 1503 a. (FIG. 22B) The spin coating methodis employed as a means of doping nickel in Embodiment 6. However, othermethods such as evaporation and sputtering may be used for forming athin film containing a metal element (nickel film in the case ofEmbodiment 6) on the amorphous semiconductor film.

[0207] Employing the method of irradiating a laser stated in theembodiment mode of the present invention, a crystalline silicon film1802 is formed next. (FIG. 22C)

[0208] By performing the rest of the process in accordance with thesteps after FIG. 15C indicated in Embodiment 5, the structure shown inFIG. 21 can be attained

[0209] If an island-like semiconductor layer is manufactured from theamorphous silicon film crystallized by using a metal element as inEmbodiment 6, a very small amount of the metal element will remain inthe island-like semiconductor film. Of course, it is still possible tocomplete a TFT under this state, but preferably better to remove atleast the nickel element that will remain in a channel-forming region.As a means of removing the catalyst element residue, there is a methodof utilizing a gettering action of phosphorus (P). A step in whichphosphorus is selectively doped, heated, and gettered may be added.Nonetheless, without the addition of such step, the concentration ofphosphorus (P) necessary for gettering is approximately the same levelas the concentration in the impurity region (n⁺) formed in FIG. 17B.Accordingly, by means of the heat treatment in the activation step shownin FIG. 17D, the catalyst element in the channel-forming region of then-channel type TFT and the p-channel type TFT can be gettered therefrom.

[0210] There are other means for removing the catalyst element withoutbeing particularly limited. For example, after forming the island-shapesemiconductor layer, heat treatment is performed on the crystallinesemiconductor film with a catalyst element residue at a temperaturebetween 800° C. and 1150° C. (preferably between 900° C. and 1000° C.)for 10 minutes to 4 hours (preferably between 30 minutes and 1 hour) inan oxygenous atmosphere to which 3 to 10 volume % of hydrogen chlorideis contained. Through this step, the nickel in the crystallinesemiconductor film becomes a volatile chloride compound (nickelchloride) and is eliminated in the treatment atmosphere during theoperation. In other words, it is possible to remove nickel by thegettering action of a halogen element.

[0211] A plural number of means may be used in combination to remove thecatalyst element. Also, gettering may be performed prior to theformation of the island-like semiconductor layer.

[0212] Embodiment 7

[0213] Referring to FIGS. 23A to 23D, an example of using another methodof crystallization, substituting the crystallization step in Embodiment5, is shown here in Embodiment 7.

[0214] First, the state of FIG. 23A is obtained in accordance withEmbodiment 5. Note that FIG. 23A corresponds to FIG. 15A.

[0215] First, an aqueous solution containing a catalyst element (nickel,in this Embodiment) (aqueous nickel acetate solution) is applied to anamorphous silicon film by spin coating to form acatalyst-element-containing layer 1902 on the entire surface of anamorphous semiconductor film 1503 a. (FIG. 23 B) Possible metal elementsother than nickel (Ni) that can be used here are elements such asgermanium (Ge), iron (Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt(Co), platinum (Pt), copper (Cu), and gold (Au).

[0216] The spin coating method is employed as a means of doping nickelin Embodiment 7. However, other methods such as evaporation andsputtering may be used for forming a thin film made of a catalystelement (nickel film in the case of Embodiment 7) on the amorphoussemiconductor film. Though the example of forming thecatalyst-element-containing layer 1902 on the entire surface of theamorphous semiconductor film 1503 a is shown here in Embodiment 7, amask may be formed to selectively form the catalyst-element-containinglayer.

[0217] Heat treatment is performed next at a temperature between 500° C.and 650° C. (preferably between 550° C. and 600° C.) for a duration of 6hours to 16 hours (preferably between 8 and 14 hours). Consequently,crystallization is advanced and a crystalline semiconductor film(crystalline silicon film in Embodiment 7) 1902 is formed. (FIG. 23 C)In the case of selectively forming the metal-element-containing layer,with an opening of the mask as the starting point, crystallizationadvances in the direction substantially parallel (the directionindicated by an arrow) with the substrate. A crystalline silicon filmthat has uniform (even) crystal growth direction when viewedmacroscopically is thus formed.

[0218] There are many defects included in the crystalline silicon filmcrystallized by the above method due to the low crystallizationtemperature, and there are cases in which it is insufficient for use asa semiconductor element material. Thus, in order to increase thecrystallinity of the crystalline silicon film, the film is irradiatedwith a laser beam using the laser irradiation method indicated in theembodiment mode of the present:invention. A crystalline silicon film1903 having good crystallinity is thus formed. (FIG. 23 D)

[0219] By performing the rest of the process in accordance with thesteps after FIG. 15C indicated in Embodiment 5, the structure shown inFIG. 21 can be attained.

[0220] Note that similar to Embodiment 6, it is further preferable toremove the catalyst element that will remain at least from thechannel-forming region. Accordingly, it is also desirable that getteringbe performed by using the method indicated in Embodiment 5.

[0221] Embodiment 8

[0222] The structure of an active matrix type liquid crystal displaydevice indicated in Embodiment 5 is explained using the perspective viewof FIG. 24. Note that in order to give correspondence with the diagramsof FIGS. 15A to 20, common symbols are used for FIG. 24.

[0223] In FIG. 24, an active matrix substrate is structured by a displayregion 1706, a scanning signal drive circuit 1704, and an image signaldrive circuit 1705 formed on a glass substrate 1501. A pixel TFT 1604 isprovided in the display region, and the drive circuits formed in theperiphery thereof are structured with CMOS circuit as a base. Thescanning signal drive circuit 1704 and the image signal drive circuit1705 are connected to the pixel TFT 1604 by a gate wiring 1548 and asource wiring 1554, respectively. Further, an FPC71 is connected to anexternal input terminal 72, and is connected via input wirings 73 and 74to the respective drive circuits. Reference symbol 1702 denotes anopposing substrate 1702.

[0224] Embodiment 9

[0225] An example of manufacturing an EL display (electroluminescence)using the present invention is explained in this embodiment.

[0226]FIG. 25A is a top view of an EL display device using the presentinvention. In FIG. 25A, reference numeral 4010 is a substrate, referencenumeral 4011 is a pixel portion, reference numeral 4012 is a sourcesignal side driver circuit, and reference numeral 4013 is a gate signalside driver circuit. Each driver circuits are connected to externalequipment, through an FPC 4017, via wirings 4014 to 4016.

[0227] A covering material 6000, a sealing material (also referred to asa housing material) 7000, and an airtight sealing material (a secondsealing material) 7001 are formed so as to enclose at least the pixelportion, preferably the driver circuits and the pixel portion, at thispoint.

[0228] Further, FIG. 25B is a cross sectional structure of the ELdisplay device of the present invention. A driver circuit TFT 4022 (notethat a CMOS circuit in which an n-channel. TFT and a p-channel TFT arecombined is shown in the figure here), a pixel portion TFT 4023 (notethat only an EL driver TFT for controlling the current flowing to an ELelement is shown here) are formed on a base film 4021 on a substrate4010. The TFTs may be formed using a known structure (a top gatestructure or a bottom gate structure).

[0229] This invention can be applied to the driver circuit 4022 and thepixel portion TFT 4023.

[0230] After the driver circuit TFT 4022 and the pixel portion TFT 4023are completed, a pixel electrode 4027 made from a transparent conductivefilm connected to a drain of pixel portion TFT 4023 is formed on aninterlayer insulating film (leveling film) 4026 made from a resinmaterial. An indium oxide and tin oxide compound (referred to as ITO) oran indium oxide and zinc oxide compound can be used as the transparentconducting film. An insulating film 4028 is formed after forming thepixel electrode 4027, and an open portion is formed on the pixelelectrode 4027.

[0231] An EL layer 4029 is formed next. The EL layer 4029 may be formedhaving a lamination structure, or a single layer structure, by freelycombining known EL materials (such as a hole injecting layer, a holetransporting layer, a light emitting layer, an electron transportinglayer, and an electron injecting layer). A known technique may be usedto determine which structure to use. Further, EL materials exist as lowmolecular weight materials and high molecular weight (polymer)materials. Evaporation is used when using a low molecular weightmaterial, but it is possible to use easy methods such as spin coating,printing, and ink jet printing when a high molecular weight material isemployed.

[0232] In this embodiment, the EL layer is formed by evaporation using ashadow mask. Color display becomes possible by forming emitting layers(a red color emitting layer, a green color emitting layer, and a bluecolor emitting layer), capable of emitting light having differentwavelengths, for each pixel using a shadow mask. In addition, methodssuch as a method of combining a charge coupled layer (CCM) and colorfilters, and a method of combining a white color light emitting layerand color filters may also be used. Of course, the EL display device canalso be made to emit a single color of light.

[0233] After forming the EL layer 4029, a cathode 4030 is formed on theEL layer. It is preferable to remove as much as possible any moisture oroxygen existing in the interface between the cathode 4030 and the ELlayer 4029. It is therefore necessary to use a method of depositing theEL layer 4029 and the cathode 4030 in an inert gas atmosphere or withina vacuum. The above film deposition becomes possible in this embodimentby using a multi-chamber method (cluster tool method) film depositionapparatus.

[0234] Note that a lamination structure of a LiF (lithium fluoride) filmand an Al (aluminum) film is used in this embodiment as the cathode4030. Specifically, a 1 nm thick LiF (lithium fluoride) film is formedby evaporation on the EL layer 4029, and a 300 nm thick aluminum film isformed on the LiF film. An MgAg electrode, a known cathode material, mayof course also be used. The wiring 4016 is then connected to the cathode4030 in a region denoted by reference numeral 4031. The wiring 4016 isan electric power supply line for imparting a predetermined voltage tothe cathode 4030, and is connected to the FPC 4017 through a conductingpaste material 4032.

[0235] In order to electrically connect the cathode 4030 and the wiring4016 in the region denoted by reference numeral 4031, it is necessary toform a contact hole in the interlayer insulating film 4026 and theinsulating film 4028. The contact holes may be formed at the time ofetching the interlayer insulating film 4026 (when forming a contact holefor the pixel electrode) and at the time of etching the insulating film4028 (when forming the opening portion before forming the EL layer).Further, when etching the insulating film 4028, etching may be performedall the way to the interlayer insulating film 4026 at one time. A goodcontact hole can be formed in this case, provided that the interlayerinsulating film 4026 and the insulating film 4028 are the same resinmaterial.

[0236] A passivation film 6003, a filling material 6004, and thecovering material 6000 are formed covering the surface of the EL elementthus made.

[0237] In addition, the sealing material 7000 is formed between thecovering material 6000 and the substrate 4010, so as to surround the ELelement portion, and the airtight sealing material (the second sealingmaterial) 7001 is formed on the outside of the sealing material 7000.

[0238] The filling material 6004 functions as an adhesive for bondingthe covering material 6000 at this point. PVC (polyvinyl chloride),epoxy resin, silicone resin, PVB (polyvinyl butyral), and EVA (ethylenevinyl acetate) can be used as the filling material 6004. If a dryingagent is formed on the inside of the filling material 6004, then it cancontinue to maintain a moisture absorbing effect, which is preferable.

[0239] Further, spacers may be contained within the filling material6004. The spacers may be a powdered substance such as BaO, giving thespacers themselves the ability to absorb moisture.

[0240] When using spacers, the passivation film 6003 can relieve thespacer pressure. Further, a film such as a resin film can be formedseparately from the passivation film 6003 to relieve the spacerpressure.

[0241] Furthermore, a glass plate, an aluminum plate, a stainless steelplate, an FRP (fiberglass-reinforced plastic) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, and an acrylic film canbe used as the covering material 6000. Note that if PVB or EVA is usedas the filling material 6004, it is preferable to use a sheet with astructure in which several tens of μm of aluminum foil is sandwiched bya PVF film or a Mylar film.

[0242] However, depending upon the light emission direction from the ELdevice (the light radiation direction), it is necessary for the coveringmaterial 6000 to have light transmitting characteristics.

[0243] Further, the wiring 4016 is electrically connected to the FPC4017 through a gap between the sealing material 7000, the sealingmaterial 7001 and the substrate 4010. Note that although an explanationof the wiring 4016 has been made here, the wirings 4014 and 4015 arealso electrically connected to the FPC 4017 by similarly passingunderneath the sealing material 7001 and sealing material 7000.

[0244] Embodiment 10

[0245] In this embodiment, an example of manufacturing an EL displaydevice having a structure which differs from that of Embodiment 9 isexplained using FIGS. 26A and 26B. Parts having the same referencenumerals as those of FIGS. 25A and 25B indicate the same portions, andtherefore an explanation of those parts is omitted.

[0246]FIG. 26A is a top view of an EL display device of this embodiment,and FIG. 26B shows a cross sectional diagram in which FIG. 26A is cutalong the line A-A′.

[0247] In accordance with Embodiment 9, manufacturing is performedthrough the step of forming the passivation film 6003 covering the ELelement.

[0248] In addition, the filling material 6004 is formed so as to coverthe EL element. The filling material 6004 also-functions as an adhesivefor bonding the covering material 6000. PVC (polyvinyl chloride), epoxyresin, silicone resin, PVB (polyvinyl butyral), and EVA (ethylene vinylacetate) can be used as the filling material 6004. If a drying agent isprovided on the inside of the filling material 6004, then it cancontinue to maintain a moisture absorbing effect, which is preferable.

[0249] Further, spacers may be contained within the filling material6004. The spacers may be a powdered substance such as BaO, giving thespacers themselves the ability to absorb moisture.

[0250] When using spacers, the passivation film 6003 can relieve thespacer pressure. Further, a film such as a resin film can be formedseparately from the passivation film 6003 to relieve the spacerpressure.

[0251] Furthermore, a glass plate, an aluminum plate, a stainless steelplate, an FRP (fiberglass-reinforced plastic) plate, a PVF (polyvinylfluoride) film, a Mylar film, a polyester film, and an acrylic film canbe used as the covering material 6000. Note that if PVB or EVA is usedas the filler material 6004, it is preferable to use a sheet with astructure in which several tens of μm of aluminum foil is sandwiched bya PVF film or a Mylar film.

[0252] However, depending upon the light emission direction from the ELdevice (the light radiation direction), it is necessary for the coveringmaterial 6000 to have light transmitting characteristics.

[0253] After bonding the covering material 6000 using the fillingmaterial 6004, the frame material 6001 is attached so as to cover thelateral surfaces (exposed surfaces) of the filling material 6004. Theframe material 6001 is bonded by the sealing material (which functionsas an adhesive) 6002. It is preferable to use a light hardening resin asthe sealing material 6002 at this point, but provided that the heatresistance characteristics of the EL layer permit, a thermal hardeningresin may also be used. Note that it is preferable that the sealingmaterial 6002 be a material which, as much as possible, does nottransmit moisture and oxygen. Further, a drying agent may also be addedto an inside portion of the sealing material 6002.

[0254] The wiring 4016 is electrically connected to the FPC 4017 througha gap between the sealing material 6002 and the substrate 4010. Notethat although an explanation of the wiring 4016 has been made here, thewirings 4014 and 4015 are also electrically connected to the FPC 4017 bysimilarly passing underneath the sealing material 6002.

[0255] Embodiment 11

[0256] The present invention can be applied to the EL display panel withthe structure of Embodiments 9 and 10. FIG. 27 shows a more detailedcross-sectional structure of the pixel portion. FIG. 28A shows a topview thereof, and FIG. 28B shows a circuit diagram thereof. In FIGS. 27,28A, and 28B, the same components are denoted with the same referencenumerals.

[0257] In FIG. 27, a TFT 3502 for switching provided on a substrate 3501is formed by using the NTFT according to the present invention. (SeeEmbodiments 1 to 8) In this embodiment, the TFT has a double-gatestructure. Since there is no substantial difference in its structure andproduction process, its description will be omitted. Due to thedouble-gate structure, there is an advantage in that substantially twoTFTs are connected in series to reduce an OFF current value. In thisembodiment, the TFT has a double-gate structure; however, it may have asingle gate structure, a triple gate structure, or a multi-gatestructure having 4 or more gates. Alternatively, PTFT according to thepresent invention may be used.

[0258] A current controlling TFT 3503 is formed by using the NTFT of thepresent invention. A drain wiring 35 of the switching TFT 3502 iselectrically connected to a gate electrode 37 of the current controllingTFT by a wiring 36. Furthermore, a wiring 38 is a gate wiringelectrically connected to gate electrodes 39 a and 39 b of the switchingTFT 3502.

[0259] At this time, it is very important that the current control TFT3503 has a structure according to the present invention. The currentcontrolling TFT functions for controlling the amount of a currentflowing through an EL element, so that the TFT is likely to be degradedby heat and hot carriers due to a large amount of current flowntherethrough. Therefore, the structure of the present invention is veryeffective, in which an LDD region is provided on the drain side of thecurrent controlling TFT so as to overlap the gate electrode via the gateinsulating film.

[0260] Furthermore, in this embodiment, the current controlling TFT 3503has a single gate structure. However, it may have a multi-gate structurein which a plurality of TFTs are connected in series. Furthermore, itmay also be possible that a plurality of TFTs are connected in parallelto substantially divide a channel formation region into a plurality ofparts, so as to conduct highly efficient heat release. Such a structureis effective for preventing degradation due to heat.

[0261] As shown in FIG. 28A, a line to be the gate electrode 37 of thecurrent controlling TFT 3503 overlaps a drain wiring 40 of the currentcontrolling TFT 3503 via an insulating film in a region 3504. In theregion 3504, a capacitor is formed.

[0262] The capacitor 3504 functions for holding a voltage applied to agate of the current controlling TFT 3503. The drain line 40 is connectedto a current supply line (power source line) 3506 so as to be alwayssupplied with a constant voltage.

[0263] A first passivation film 41 is provided on the switching TFT 3502and the current controlling TFT 3503, and a flattening film 42 that ismade of a resin insulating film is formed thereon. It is very importantto flatten the step difference due to TFTs by using the flattening film42. The step difference may cause a light-emitting defect because the ELlayer to be formed later is very thin. Thus, it is desirable to flattenthe step difference so that the EL layer is formed on a flat surfacebefore forming a pixel electrode.

[0264] Reference numeral 43 denotes a pixel electrode (cathode of an ELelement) that is made of a conductive film with high reflectivity and iselectrically connected to the drain of the current controlling TFT 3503.As the pixel electrode 43, a low resistant conductive film such as analuminum alloy film, a copper alloy film, and a silver alloy film, or alayered structure thereof can be preferably used. Needless to say, alayered structure with other conductive films may also be used.

[0265] A light-emitting layer 45 is formed in a groove (corresponding toa pixel) formed by banks 44 a and 44 b made of an insulating film(preferably resin). Herein, only one pixel is shown; however,light-emitting layers corresponding to each color ® (red), G (green),and B (blue)) may be formed. As an organic EL material for thelight-emitting layer, a π-conjugate polymer material is used. Examplesof the polymer material include polyparaphenylene vinylene (PPV),polyvinyl carbazole (PVK), and polyfluorene.

[0266] There are various types of PPV organic EL materials. For example,materials as described in “H. Shenk, Becker, O. Gelsen, E. Kluge, W.Kreuder and H. Spreitzer, “Polymers for Light Emitting Diodes”, EuroDisplay, Proceedings, 1999, pp. 33-37” and Japanese Laid-OpenPublication No. 10-92576 can be used.

[0267] More specifically, as a light-emitting layer emitting red light,cyanopolyphenylene vinylene may be used. As a light-emitting layeremitting green light, polyphenylene vinylene may be used. As alight-emitting layer emitting blue light, polyphenylene vinylene orpolyalkyl phenylene may be used. The film thickness may be prescribed tobe 30 to 150 nm (preferably 40 to 100 nm).

[0268] The above-mentioned organic EL materials are merely examples foruse as a light-emitting layer. The present invention is not limitedthereto. A light-emitting layer, a charge-transporting layer, or acharge injection layer may be appropriately combined to form an EL layer(for light emitting and moving carriers therefor).

[0269] For example, in this embodiment, the case where a polymermaterial is used for the light-emitting layer has been described.However, a low molecular-weight organic EL material may be used.Furthermore, an inorganic material such as silicon carbide can also beused for a charge-transporting layer and a charge injection layer. Asthese organic EL materials and inorganic materials, known materials canbe used.

[0270] In this embodiment, an EL layer with a layered structure is used,in which a hole injection layer 46 made of PEDOT (polythiophene) or PAni(polyaniline) is provided on the light-emitting layer 45. An anode 47made of a transparent conductive film is provided on the hole injectionlayer 46. In this embodiment, light generated by the light-emittinglayer 45 is irradiated to the upper surface (toward TFTs), so that theanode 47 must be transparent to light. As a transparent conductive film,a compound of indium oxide and tin oxide, and a compound of indium oxideand zinc oxide can be used. The conductive film is formed after formingthe light-emitting layer and the hole injection layer with low heatresistance, so that the conductive film that can be formed at a possiblylow temperature is preferably used.

[0271] When the anode 47 is formed, the EL element 3505 is completed.The EL element 3505 refers to a capacitor composed of the pixelelectrode (cathode) 43, the light-emitting layer 45, the hole injectionlayer 46, and the anode 47. As show in FIG. 28A, the pixel electrode 43substantially corresponds to the entire area of a pixel. Therefore, theentire pixel functions as an EL element. Thus, a light image displaywith very high light use efficiency can be performed.

[0272] In this embodiment, a second passivation film 48 is furtherformed on,the anode 47. As the second passivation film 48, a siliconnitride film or a silicon nitride oxide film is preferably used. Thepurpose of the passivation film 48 is to prevent the EL element frombeing exposed to the outside. That is, the passivation film 48 protectsan organic EL material from degradation due to oxidation, and suppressesthe release of gas from the organic EL material. Because of this, thereliability of the EL display device is enhanced.

[0273] As described above, the EL display panel of the present inventionhas a pixel portion made of a pixel with a structure as shown in FIG.27, and includes a switching TFT having a sufficiently low OFF currentvalue and a current controlling TFT that is strong to the injection ofhot carriers. Thus, an EL display panel is obtained, which has highreliability and is capable of displaying a satisfactory image.

[0274] This embodiment can be realized by being appropriately combinedwith the structures of Embodiments 1 to 8. Furthermore, it is effectiveto use the EL display panel of this embodiment as a display portion ofelectronic equipment.

[0275] Embodiment 12

[0276] In this embodiment, referring to FIG. 29, the case will bedescribed where the structure of the EL element 3505 is reversed in thepixel portion described in Embodiment 11. The difference from thestructure shown in FIG. 27 lies only in the EL element and the currentcontrolling TFT, so that the description of the other parts will beomitted.

[0277] In FIG. 29, a current controlling TFT 3503 is formed of a PTFTaccording to the present invention. Regarding the production process,Embodiments 1 to 8 should be referred to.

[0278] In this embodiment, a transparent conductive film is used as apixel electrode (anode) 50. More specifically, a conductive film made ofa compound of indium oxide and zinc oxide is used. Needless to say, aconductive film made of a compound of indium oxide and tin oxide may beused.

[0279] After banks 51 a and 51 b made of an insulating film are formed,a light-emitting layer 52 made of polyvinyl carbazole is formed bycoating of a solution. On the light-emitting layer 52, an electroninjection layer 53 made of potassium acetyl acetonate (acacK), and acathode 54 made of an aluminum alloy are formed. In this case, thecathode 54 functions as a passivation film. Thus, an EL element 3701 isformed.

[0280] In this embodiment, light generated by the light-emitting layer52 is irradiated toward the substrate on which a TFT is formed asrepresented by an arrow.

[0281] This embodiment can be realized by being appropriately combinedwith the structures of Embodiments 1 to 8. Furthermore, it is effectiveto use the EL display panel of this embodiment as a display portion ofelectronic equipment.

[0282] Embodiment 13

[0283] In this embodiment, referring to FIGS. 30A to 30C, the case willbe described where a pixel having a structure different from that of thecircuit diagram shown in FIG. 28B is used. Reference numeral 3801denotes a source line of a switching TFT 3802, 3803 denotes a gatewiring of the switching TFT 3802, 3804 denotes a current controllingTFT, 3805 denotes a capacitor, 3806 and 3808 denote current supplylines, and 3807 denotes an EL element.

[0284]FIG. 30A shows the case where two pixels share the current supplyline 3806. More specifically, two pixels are formed so as to beaxisymmetric with respect to the current supply line 3806. In this case,the number of power supply lines can be reduced, so that the pixelportion is allowed to have a higher definition.

[0285] Furthermore, FIG. 30B shows the case where the current supplyline 3808 and the gate line 3803 are provided in parallel. In FIG. 30B,although the current supply line 3808 does not overlap the gate wiring3803, if both lines are formed on different layers, they can be providedso as to overlap each other via an insulating film. In this case, thecurrent supply line 3808 and the gate line 3803 can share an occupiedarea, so that a pixel portion is allowed to have higher definition.

[0286] Furthermore, FIG. 30C shows the case where the current supplyline 3808 and gate wiring 3803 are provided in parallel in the same wayas in FIG. 30B, and two pixels are formed so as to be axisymmetric withrespect to the current supply line 3808. It is also effective to providethe current supply line 3808 so as to overlap one of the gate wiring3803. In this case, the number of the power supply lines can be reduced,so that a pixel portion is allowed to have higher definition.

[0287] This embodiment can be realized by being appropriately combinedwith the structures of Embodiments 1 to 10. Furthermore, it is effectiveto use the EL display panel of this embodiment as a display portion ofelectronic equipment.

[0288] Embodiment 14

[0289] In FIGS. 28A and 28B shown in Embodiment 11, the capacitor 3504is provided so as to hold a voltage applied to a gate of the currentcontrolling TFT 3503. However, the capacitor 3504 can be omitted. InEmbodiment 11, since the NTFT according to the present invention asshown in Embodiment 1 to 8 is used as the current controlling TFT 3503,the TFT 3503 has an LDD region provided so as to overlap a gateelectrode via a gate insulating film. In this region, a parasiticcapacitor called a gate capacitor is generally formed. This embodimentis characterized in that the parasitic capacitor is used in place of thecapacitor 3504.

[0290] The capacitance of the parasitic capacitor is varied dependingupon the area in which the above-mentioned gate electrode overlaps theLDD region. Therefore, the capacitance is determined by the length ofthe LDD region included in the region positively.

[0291] Similarly, in FIGS. 30A, 30B, and 30C, the capacitor 3805 canalso be omitted.

[0292] This embodiment can be realized by being appropriately combinedwith the structures of Embodiments 1 to 13. Furthermore, it is effectiveto use an EL display panel having a pixel structure of this embodimentas a display portion of electronic equipment.

[0293] Embodiment 15

[0294] The CMOS circuit and the pixel portion formed by implementing thepresent invention can be used in various electro-optical devices (activematrix type liquid crystal display device, active matrix EL displaydevice, and active matrix EC display). That is, the present inventioncan be implemented in all electronic equipment that incorporate theseelectro-optical devices as a display portion.

[0295] The following can be given as such electronic equipment: a videocamera, a digital camera, a projector (a rear type or a front type), ahead mount display (goggle type display), a car navigation system, a carstereo, a personal computer, a portable information terminal (such as amobile computer, a cellular phone, and an electronic book) etc. Someexamples of these are shown in FIG. 31, FIG. 32 and FIG. 33.

[0296]FIG. 31A shows a personal computer that is comprised of a mainbody 2001, an image input portion 2002, a display portion 2003, and akeyboard 2004. The present invention can be applied to the image inputportion 2002, the display portion 2003 and the other signal controlcircuit.

[0297]FIG. 31B shows a video camera that is comprised of a main body2101, a display portion 2102, an audio input portion 2103, operationswitches 2104, a battery 2105, and an image receiving portion 2106. Thepresent invention can be applied to the display portion 2102, and othersignal control circuit.

[0298]FIG. 31C shows a mobile computer that is composed of a main body2201, a camera portion 2202, an image receiving portion 2203, operationswitches 2204, and a display portion 2205. The present invention can beapplied to the display portion 2205 and other signal control circuit.

[0299]FIG. 31D shows a goggle type display that is comprised of a mainbody 2301, display portions 2302, and arm portions 2303. The presentinvention can be applied to the display portion 2302 and other signalcontrol circuit.

[0300]FIG. 31E shows a player which uses a recording medium in which aprogram is stored (hereinafter referred to as a recording medium) andwhich is comprised of a main body 2401, a display portion 2402, speakerportions 2403, a recording medium 2404, and operation switches 2405. ADVD (Digital Versatile Disc), a CD or the like is used as the recordingmedium to enable the player to appreciate music and the movies, and playa game or the Internet. The present invention can be applied to thedisplay portion 2402 and other signal control circuit.

[0301]FIG. 31F shows a digital camera that is comprised of a main body2501, a display portion 2502, an eye-piece portion 2503, operationswitches 2504, and an image receiving portion (not shown in the figure).The present invention can be applied to the display portion 2502 andother signal control circuit.

[0302]FIG. 32A shows a front type projector that is comprised of aprojection unit 2601, a screen 2602, and the like. The present inventioncan be applied to a liquid crystal display device 2808 which is a partstructuring the projection unit 2601 and other signal control circuit.

[0303]FIG. 32B shows a rear type projector that is comprised of a mainbody 2701, a projection unit 2702, a mirror 2703, a screen 2704, and thelike. The present invention can be applied to the liquid crystal displaydevice 2808 which is a part structuring the projection unit 2702 andother signal control circuit.

[0304] Illustrated in FIG. 32C is an example of the structure of theprojection units 2601 and 2702 that are shown in FIGS. 32A and 32B,respectively. Each of the projection units 2601 and 2702 is comprised ofa light source optical system 2801, mirrors 2802 and 2804 to 2806,dichroic mirrors 2803, a prism 2807, liquid crystal display devices2808, phase difference plates 2809, and a projection optical system2810. The projection optical system 2810 is constructed of an opticalsystem including projection lenses. An example of a three plate systemis shown in the present embodiment, but there are no speciallimitations. For instance, an optical system of single plate system isacceptable. Further, the operator may suitably set optical systems suchas optical lenses, polarizing film, film to regulate the phasedifference, IR film, within the optical path shown by the arrows in FIG.32C.

[0305] In addition, FIG. 32D shows an example of the structure of thelight source optical system 2801 of FIG. 32C. In the present embodiment,the light source optical system 2801 is composed of a reflector 2811, alight source 2812, a lens array 2813 and 2814, a polarizing conversionelement 2815, and a condenser lens 2816. Note that the light sourceoptical system shown in FIG. 32D is an example, and it is not limited tothe illustrated structure. For example, the operator may suitably setoptical systems such as optical lenses, polarizing film, film toregulate the phase difference, and IR film.

[0306] The projector illustrated in FIG. 32, show the electro opticaldevice of transparent type but the example of the electro optical deviceof reflection type and the EL display device.

[0307]FIG. 33A shows a cellular phone that is comprised of a main body2901, an audio output portion 2902, an audio input portion 2903, adisplay portion 2904, an operation switches 2905 and an antenna 2906etc. The present invention can be applied to the audio output portion2902, the audio input portion 2903, the display portion 2904 and othersignal control circuit.

[0308]FIG. 33B shows a mobile book (electronic book) that is comprisedof a main body 3001, a display portion 3002, 3003, a recording medium3004, an operation switches 3005 and a antenna 3006 etc. The presentinvention can be applied to the display portion 3002, 3003 and othersignal control circuit.

[0309]FIG. 33C shows a display that is comprised of a main body 3101, asupport stand 3102 and display portion 3103 etc. The present inventioncan be applied to the display portion 3103. They are especiallyadvantageous for cases in which the screen is made large, and isfavorable for displays having a diagonal greater than or equal to 10inches (especially one which is greater than or equal to 30 inches).

[0310] Thus, the application range for the present invention isextremely wide, and it may be applied to electronic equipment in allfields. Further, the electronic equipment of this Embodiment can berealized with a composition that uses any combination of Embodiments 1to 14.

[0311] The provision of a high cost performance laser irradiationprocess can be attained by the laser irradiation apparatus of thepresent invention. In addition, laser beams having a higher uniformitycan be obtained through the present invention. The laser irradiationapparatus provided by the present invention can be utilized in processessuch as the crystallization process of the non-single crystal siliconfilm.

What is claimed is:
 1. An apparatus for irradiating a laser beam with asquare or rectangular cross-section on a surface to be irradiated, saidapparatus comprises: a laser oscillator for emitting a plurality oflaser beams having different wavelengths from each other; an opticalsystem for uniforming an energy distribution of each of said pluralityof laser beams and for processing each of said plurality of laser beamshaving different wavelengths from each other into said square orrectangular cross-section on said surface to be irradiated; and a stageover which an object to be irradiated is disposed.
 2. An apparatusaccording to claim 1 wherein said laser oscillator is a YAG laser.
 3. Anapparatus according to claim 1 wherein said laser oscillator is azigzag-slab-style YAG laser.
 4. An apparatus according to claim 1wherein said object is a non-single crystal semiconductor filmcomprising silicon.
 5. An apparatus according to claim 1 wherein saidplurality of laser beams having different wavelengths from each othercomprise second and third harmonics of a YAG laser beam.
 6. An apparatusaccording to claim 1 wherein said plurality of laser beams havingdifferent wavelengths from each other comprise second and fourthharmonics of a YAG laser beam.
 7. An apparatus according to claim 1wherein said plurality of laser beams having different wavelengths fromeach other comprise third and fourth harmonics of a YAG laser beam. 8.An apparatus according to claim 1 wherein each of said plurality oflaser beams having different wavelengths from each other has awavelength of 600 nm or less.
 9. An apparatus according to claim 1further comprising: a load/unload chamber; a transfer chamber; a robotarm; and a laser irradiation chamber.
 10. An apparatus for irradiating alaser beam with a linear cross-section on a surface to be irradiated,said apparatus comprising: a laser oscillator for emitting a pluralityof laser beams having different wavelengths from each other; an opticalsystem for uniforming an energy distribution of each of said pluralityof laser beams and for processing each of said plurality of laser beamshaving different wavelengths from each other into a linearcross-section; and means for moving an object to be irradiatedrelatively to said plurality of laser beams.
 11. An apparatus accordingto claim 10 wherein said laser oscillator is a YAG laser.
 12. Anapparatus according to claim 10 wherein said laser oscillator is azigzag-slab-style YAG laser.
 13. An apparatus according to claim 10wherein said object is a non-single crystal semiconductor filmcomprising silicon.
 14. An apparatus according to claim 10 wherein saidplurality of laser beams having different wavelengths from each othercomprise second and third harmonics of a YAG laser beam.
 15. Anapparatus according to claim 10 wherein said plurality of laser beamshaving different wavelengths from each other comprise second and fourthharmonics of a YAG laser beam.
 16. An apparatus according to claim 10wherein said plurality of laser beams having different wavelengths fromeach other comprise third and fourth harmonics of a YAG laser beam. 17.An apparatus according to claim 10 wherein each of said plurality oflaser beams having different wavelengths from each other has awavelength of 600 nm or less.
 18. An apparatus according to claim 10further comprising: a load/unload chamber; a transfer chamber; a robotarm; and a laser irradiation chamber.
 19. A laser beam irradiationmethod comprising: irradiating a plurality of laser beams havingdifferent wavelengths from each other on a same region simultaneously,wherein each of said plurality of laser beams has a square orrectangular cross section on said same region.
 20. A method according toclaim 19 wherein said laser oscillator is a YAG laser.
 21. A methodaccording to claim 19 wherein said plurality of laser beams havingdifferent wavelengths from each other comprise second and thirdharmonics of a YAG laser beam.
 22. A method according to claim 19wherein said plurality of laser beams having different wavelengths fromeach other comprise second and fourth harmonics of a YAG laser beam. 23.A method according to claim 19 wherein said plurality of laser beamshaving different wavelengths from each other comprise third and fourthharmonics of a YAG laser beam.
 24. A method according to claim 19wherein each of said plurality of laser beams having differentwavelengths from each other has a wavelength of 600 nm or less.
 25. Alaser beam irradiation method comprising: preparing a non single crystalsemiconductor film formed over a substrate; and irradiating a pluralityof laser beams having different wavelengths from each other onto a sameregion of said semiconductor film simultaneously, wherein each of saidplurality of laser beams has a square or rectangular cross-section onsaid same region.
 26. A method according to claim 25 wherein said laseroscillator is a YAG laser.
 27. A method according to claim 25 whereinsaid plurality of laser beams having different wavelengths from eachother comprise second and third harmonics of a YAG laser beam.
 28. Amethod according to claim 25 wherein said plurality of laser beamshaving different wavelengths from each other comprise second and fourthharmonics of a YAG laser beam.
 29. A method according to claim 25wherein said plurality of laser beams having different wavelengths fromeach other comprise third and fourth harmonics of a YAG laser beam. 30.A method according to claim 25 wherein each of said plurality of laserbeams having different wavelengths from each other has a wavelength of600 nm or less.